Color fill in Photoshop for iPad

Hello,

TL;DR - How can I change the "color fill" color?

Just yesterday I purchased my iPad Pro and immediately installed Photoshop, instantly transferred my PSD project from my iMac and started working, but I ran into my first wall… my layers consist of many "Color Fill"s since I am colorizing an old black and white photo, and I just couldn't change the fill color in my layer, whatever I tried it just doesn't seem to respond.

What am I doing wrong?  how do I change the color inside my solid color layer?
In the meantime I am using Sidecar and working on the desktop version of Photoshop.

Thanks!