I've asked a question on the unity forum and I have sent a support email to you directly and haven't heard back from either. I did this many weeks ago. I haven't reviewed the asset yet because I do not want to rush to judgment, but I would like to review it soon.
I kind of figured it out. Not sure if there is a better way of doing this. But here is the what I used. I have a texture file with four different eyes. I wanted to select one set and change only the eye color. I had to use sharpen I have an issue with the texture artifacts giving me some gray pixels messing up the threshold.
We simplify and made a Damage FX node and Damage FX Tint ( to change the color ) in the new version 1.9.3
you can move it or zoom it
or add multiple damage fx on the sprite
Or use a tint to change by yourself the color