In general there are a few rules when it comes to pot colour selection that are based around aesthetics in order that your bonsai trees are displayed to their advantage.
A Beginner's Guide to Bonsai - Dengarden
Selection tips
Bonsai - Wikipedia
Bonsai Japanese Maple Tree — Mr Maple │ Buy Japanese Maple Trees
Bonsai Pots: The Ultimate Guide For Beginners
The Art of Bonsai Pot Selection: Enhancing Your Bonsai's Beauty - Bonsai Plaza
Selecting a suitable container - Bonsai Tree (Pty) Ltd.
Bonsai Pots - Selection Guide - Bonsai Trees for Beginners Series #94
Bonsai pot colour guide
Bonsai Pot Selection From a Different Perspective - Iker Bonsai Pots