From Poet Anon about coloring eyes:
I actually don't utilize gradients at all, since I suck at them. What I do is I use the Adjustments > Replace Color and Adjustments > Curves or Levels (and sometimes Exposure, Hue/Saturation, and Vibrance but honestly mostly Curves or Levels) for the entire eye. Sometimes I will apply a pair of colorful lashes or iris colors which I first made using the tools I mentioned and fiddling around with their pixel-ling (especially for white lashes) with the Pencil Tool. Then I cut them onto their own layers, and copy them as necessary for certain eye colors. If I get stubborn pixels, I will go in with either Replace Color or the Pencil Tool to manually fix it. I hope that makes sense haha, I mostly d**k around on Photoshop so I'm definitely not an expert and my way is not necessarily the right way to do things.