Problem: the curve colour is shown in the same button as the visibility eye. Since the eye is drawn in white, this can make it hard to see when the curve colour is bright.
Proposal: show the curve colour in a separate little strip on the side, and put the visibility button next to it. Some examples:
Note that it's important to keep the colour well-visible; moving the eye icon away from it shouldn't detriment from the visibility of the colour.