question Polar or Mournful/Ghostly?

Polar items are bluish white with an opalescent effect. Mournful/Ghostly items also have blue and white, but the shades of blue are that of sky blue or lily, and of periwinkle.
question Mournful/Ghostly or Winterstorm?

The term "Ghostly" was something users came up with, but Gaia has began calling all items in this scheme as "Mournful" because of the first item in this scheme, Mournful Wail. On the other hand, Winterstorm is an official Gaian name, that first appeared with the item Cabochomp.
What differentiates these 2 color schemes is the shade of color called Dark Iris. Mournful/Ghostly items do not have an Iris color, while Winterstorm is a combination of either Polar/Ghostly, and of Dark Iris. Although at times, Gaia staff tags Ghostly items with the Winterstorm tag so it gets a bit confusing.
question Ghost or Mournful/Ghostly?

The Ghost color scheme is an old color scheme that was popularized by the 2010 Halloween event (Remember NPC Pancakes?). Its colors are of turquoise and teal, and looks more of a light shade of green/mint, than that of blue. Mournful/Ghostly is more on the bluish shades of sky blue, lily and periwinkle.