The eye:
And believe it or not, I actually drew the iris from scratch in Blender’s UV/ image editor. The texture looks like this unrapped:
My basic procedure was:
1: Using large brush, fill main iris color as well as border
2: switching to fine brush (1 or 2 px) run lines back and forth through the pupil
3: repeat step 2 with different shades like brown / hazil etc.
4: Apply a smooth brush over the whole thing
5: Apply a smear brush over the whole thing
Obviously these steps could be performed differently, but the smear and smooth brush turned what looked like a 5 year old’s crayon creation into something sharp and imo realistic.
Oh and make sure to select ‘face selection masking for painting’ so you can color outside of the lines a little 