I've drawn the eye onto a good quality fabric with a mechanical pencil.
It's drawn quite lightly, I don't want the pencil line to show through when I add the other colors.
Color the pupil, you don't need to add too much color to begin with, you can layer with color later.
I use prisma color pencils for the softer areas and Derwent for the finer areas.... they are not quite as waxy as the prisma pencils.
colored pencil and and little ink...... I'm not going to give away too many of my secrets... you'll have to come to class !!!!! but I guess the pictures help.....!!!