Hello Caybang and CVMomma,
Sorry, I had not seen this thread before - I actually replied to a support ticket Caybang sent to our support website and had given this same answer:
There isn't a setting where you can easily just change the colors of the notes. We only have a setting to change between using a Fixed Do and a Movable Do, but unfortunately we don't have a function which enables you to change the color scheme for each note.
CVMomma's suggestion on changing the settings to 'non-rainbow' for solfege might be useful though, so please do explore using that setting.