Workarounds
A workaround I employ sometimes is to use the Advanced Color Selector docker instead of the toolbar color selector.
A 2nd workaround, one that doesn’t really work on mobile devices, is one could stick with the standard FG/BG icon. The difficulty is this icon has 3 functions — it opens color selectors, switches between FG and BG colors and it changes FG/BG to black and white. The Android UI is too tiny to tap on this one correctly.
A different solution perhaps could be to assign one of the unused Touch Docker spaces to a color selector but that might not be feasible. There is a reason the 2 icons on either side of the save icon do not function on Android but I can’t remember what is was. Perhaps this docker isn’t editable.
Yes, there is one that looks like 2 little squares. I use it on my Windows desktop.
That icon is not usable on Android because of the UI size problem so I removed it from the toolbar. Most of us have to turn off HiDPI and change the system font to the smallest available in order to make pop up windows work (like the brush editor).
With the UI so tiny there’s no way to tap that icon and know which of its 3 functions will be invoked (select FG/BG colour, switch FG/BG, change FG/BG to black and white).
For a long time there has been a todo item in my list, which can allow DPI scaling to be more adjustable than a simple toggle, like a slider. I wonder if having something like that would help user tweak this issue better? (of course, this is a work around not a solution)