I have this problem constantly. When I change the color of text, some or all of the text will change back to the original color. It does not happen to all text color changes (I use color a lot to classify information), but happens very frequently. I exclusively use the Mac client, and this happens across multiple computers. Steps to reproduce:
Change color of some text
Force sync with server (just to be sure it syncs)
Switch to a different note
Switch back to the original note & color has reverted back to the original
It is especially weird because sometimes only part of a sentence will change back, and other parts will not. This has been a bug for a long time, and I really wish you guys would fix it. Please contact me if you need more information about how to reproduce it.