The only two real restrictions on color scheme are these (from the CRLs):
No “modern” or “common” off-the-shelf camouflage patterns may be used. Camouflage patterns allowed must be uncommon, vintage, or in-universe and will be highly scrutinized during the application process.
No glitter paint allowed for armor or props.
That being said, there are certain colors with special significance and meaning in Mandalorian culture. In canon, these colors and their meanings are:
- Gray = Mourning a Lost Love or Family member
- Red = Honoring a Parent or leader
- Black = Justice
- Gold = Vengeance
- Green = Duty
- Blue = Reliability
- Orange = A lust for life (for Freedom)
- White = Cin Vhetin; A fresh start (lit. White Field) or Purity
Once again, though, for many, the colors chosen were just personal preferences.
If you look at the armor of the various members there, you'll find all kinds of different color schemes, some muted, some rather vibrant, some very flashy. The choice of color is up to you.