Assigning colors to individual email/calendar accounts is very important at my business. We all use the calendar daily to see what is going on. And we use the color coding for quick reference. Unfortunately when we switched from our previous calendar to yours that wasn't easily done.
I have found no way to connect a users account with another, as it pertains to maintaining proper colors.
I have attached everyone's calendar to everyone else's in a read-only fashion. That works fine. No complaints there. But I have 20 people using email, each with their own color, but initially when they see others in "their" calendar, it is not with the color that was assigned to the "other" account. Their account just randomly assigns a new color to the other user. Which is in no way related to their proper color.
This means I have to log into each account and reassign all the colors for the other accounts. So 20 accounts times 20 colors, means I had to setup the colors 400 times in order to maintain a similar setup as before.
I am not sure why when I set a color to an account, that is not seen by the others by default when I attach them. Certainly, if someone "wants" to change it after the fact that's fine. But it should not "default" to a random color initially.