Room avatar colours (default) are not consistent

### Your use case

#### What would you like to do?
The auto-avatars for rooms are not consistent colours. Rooms that are "suggested rooms" could be a colour, which then changes once you are a joined into that room?

#### Why would you like to do it?
Consistency means the app is easier to understand at a glance. "I immediately know which rooms are mine, and which are suggested because suugested is grey" eg.

#### How would you like to achieve it?
Decide and plan a colour palette for rooms across all platforms

### Have you considered any alternatives?

N/A

### Additional context

_No response_