Hi iPhone_Convert and welcome to EB:
I am assuming all the accounts you are managing are BIS and not BES? I am not aware of anything that provides a different color for each account in the catch-all Messages Inbox. The different Inbox icons is supposed to let you know what account a new email is from.
You could take a look at
Empower HTML Mail Viewer as I think the color of each account header can be made to be different, but I don't know if they have a version for the Bold OS.
Visit and post often and thanks for registering....