Hair
First lets have a look at Human hair color It is divided into simple categories
Auburn
Black
Blond
Brown
Red
Gray
White
Now the last two shouldn't come up too often unless your characters are middle aged or old. Honestly I don't see a lot of elderly people in RPs. The ones with ages that would put them in that range are either not human, undead, or immortal.
Anyhow these are simple color descriptions. One word and easy to spell. If you're looking for something to jazz those simple colors up, try describing the shine, hair texture, and hair style. Is your character's hair nice and glossy? Is it faded? Is it braided? Is it in a bun? Is it a bob cut, bowl cut, slicked back, buzz cut, crew cut? How do they keep their hair styled? and how long is it? Most people's hair goes to the middle of their back at the longer ranges. Knee length or ankle length is unheard of or extremely rare.
Now there are sub categories for hair color you should take note of as well. At least where there are proper names you can use a metal to describe the hair color:
Blond
Flaxen - Light but not whitish blond without traces of other colors
Yellow Blond - That cartoony yellow died hair
Platinum Blond - When natural, this color is almost exclusively found in children and albino people. The hair still blond but closer to white in color
Sandy Blond - Has some grayish hazel coloring to it
Strawberry Blond (Venetian) - Light reddish blond
Dirty Blond - similar to sandy blond, has strips of brown mixed in. This occurs naturally
Ash Blond - getting older, has a pale or grayish tinge to it
Dark Blond - darkest part of the blond spectrum, a shy away from light brown
Bleached Blond - that artificial light blond color that's a bit less white then platinum blond
Brown
Light brown - a light colored brown
Chestnut brown - Dark brown with a visible wine auburn highlight
Light chestnut brown - Medium to dark brown with very subtle chestnut tones
Dark Brown - fairly deep in tone and sometimes difficult to distinguish from black
Deepest brown - The darkest brown, appears to be off black at a distance
Auburn
Often mistaken for red or brown, auburn is a mix of both. It's more of a rust color.
Vivid Auburn - a color dye that makes for a brighter rust colored hair.
Red
Red hair ranges from a light red-orange to just before auburn.
Black
Black hair has a narrow range from a softer black to a dark inky color.
Gray and White
Sometimes you have a few gray hairs mixed in with the color, other times it all grays out. At a certain age, hair roots begin to lose melanin and hair will continue to grow without it.
Anyway, there's plenty of color description above. It isn't hard to find the right color to describe a character's hair. Using natural hair descriptions can be good not only for your character's development but it can have an impact on how other characters perceive them. Mary Sues aren't particularly well received. Gem/precious metal hair descriptions right off the bat are a red flag.
This may sound goofy, but if you want your hair to attract special attention, take care of it, play with it, enjoy it. Love your hair, don't just let it fall flat. Regardless of color it'll never get the attention you want if it's just a colored mop on your head. If you can toss it, comb it, and let it catch wind, it'll get you some attention.
Eyes
Eye color seems to get butchered just as much as hair color. Gemstones, precious metals, and other non-eye related objects get attributed to eyes. Here are the most common Human eye colors:
Amber - these eyes seem brown but contain a yellowish or coppery tint to them.
Blue - these eyes have a light blue color due to low amounts of melanin
Brown - the most dominant eye color in humans, brown eyes have a slight variation into light and dark
Gray - Though they have less melanin than blue eyes they appear darker and well gray
Green - green eyes are usually an olive color.
Hazel - hazel eyes appear light brown and can appear to shift to a brown green color.
This might seem like a limited spectrum, but the iris is made in varying fashions to be more speckled or reflective. The eye dilates differently from person to person, and the shape of the eyelids plays a major factor to how the eyes actually look. I think it's easier to describe how the eyes are shaped rather than just going based upon color. Is your characters eyes round? are they narrow and oval shaped? do they open wide and show a lot of white, to they open narrowly? Does the iris take up a lot of the visible eye? At the least remember that those eyes are part of a face. You can't really stick "pretty" eyes into a butt ugly face and have them still be regarded as such.
Skin
Lucky for us, a man named Felix Von Luschan created a chromatic scale for us regarding human skin.


type I: von Luschan 1-5 (very light).
type II: von Luschan 6-10 (light). Average Caucasian
type III: von Luschan 11-15 (intermediate). Dark Caucasian
type IV: von Luschan 16-21 ("Mediterranean").
type V: von Luschan 22-28 (dark or "brown").
type VI: von Luschan 29-36 (very dark or "black").
(No, these color types weren't devised by race or something discriminatory like that. They were categorized in order of sun tan/burn risk.)
Now you don't have to quote a von Luschan scale number or type to describe your character, but at least use a reasonable color to describe them.
Talk about texture too. Is their skin smooth and supple, is it bumpy and coarse, is it scaly, is it dry, is it covered in hair? Does this character have cellulite? acne? warts? eczema? vitiligo? Is their skin clear and uniform? do they have freckles all over? Try these descriptions first. Please, don't use "perfect" as a description, for ANYTHING! Perfect is quite possibly the most vague term you can use to describe anything.
Unnatural or supernatural coloring
It's not illegal or wrong to have unnatural colors for characters eye and hair color but remember we do have a color wheel.

Remember our old super friends the primary colors? Remember their satellite allies, the secondary colors? At least try them before using gemstones and/or precious metals to describe colors. After all, our friends on the color wheel were used to describe the colors of those gemstones and precious metals first.
For example, if your character's eyes are an unnatural primary red, you don't have to say they're ruby red. It isn't helping at all. Rubies aren't any redder than primary red, tomatoes, or the red on a coca-cola can. (Actually Rubies can be fairly dark in color so they might be "Less red".) Instead try letting the color describe itself and use how your characters eyes react in light. are they glassy and dull red? Does the red fade in obstructed sunlight? Do they sparkle like water in the afternoon sun? Are they slightly luminescent even in darkness?
Another example, or rant if you will, please please PLEASE DO NOT use Diamond as a color! The purest diamonds don't have a color to them! The least pure diamonds have a yellowish tinge to them. DO YOU WANT YOUR CHARACTER TO HAVE YELLOWISH TINGE CLEAR EYES WITH NOTHING BEHIND THEM?!
What I'm asking again is don't describe a description. Colors are descriptions. Unless there's true variation in the color and it doesn't have an actual name to the color, then you can describe the changes in color or relate it to an object, A MUNDANE OBJECT! Most people don't have precious gems and metals on hand to inspect and relate the colors. Those who do, can get by on the simple one word color. If you're having trouble, try getting out the crayons or colored pencils. Mix the colors and describe it using the colors you mixed.
Non human character example traits.
Orc
Well from contemporary games and story telling orcs tend to be shades of yellow green to olive green, to in some cases brown. If you've played with colors before you can mix some green and brown and get your desired Orc color. Same seems to go for Goblins and Ogres. Their hair, usually ratty, unkempt and black. Sometimes their hair is brown, auburn, or naturally gray.
Elf
Well, there's lots of kinds of elves. Brownies, (Keebler elves...), High Elves (most common), Dark elves, Drow, Elves usually are described with long straight hair, pointy ears, soft blemish-less skin, and attractive facial features. I'm being general cause those creepy D&D guys don't know what to jerk off to first... Ok that was a vicious rant but I'll get to that later. I'm sorry.
Completing the face
Well since people look to your head Usually (Ok, Ok! I'm sorry!) to define how your character looks, you should at least work on individualizing that as much as possible. Don't just jumble what features they have, find a starting point and flow across the face. Try starting with the hair and working down to the eyes, nose, ears, and chin. Or start with the eyes and work your way out to the nose, ears, chin, then hair. Don't forget the skin color and texture.
In character profile the features generally required are those of the face and hair. If you're writing, it's okay to describe body type and height first if that's what another character sees as they approach, but please unless this is from the point of view of a very rich character who ogles his or her jewelry frequently, please please PLEASE stay away from precious metals and gemstones as color descriptions.
And please remember this: Beauty is in the eye of the beholder. It's only up to you to convey how beautiful you see your character. Whether or not you can portray this effectively, if another character or player sees them as unattractive, don't take it personally. If your character is supposed to be stunningly gorgeous don't just say it. Let their features paint that picture. If they're supposed to be horridly ugly use descriptive features that make them look horridly ugly. Don't use direct descriptions like beautiful or ugly unless it's internal dialogue and the character views himself or herself that way.