Colored thread would make them easier to identify. Right now the feature isn't very friendly to use, we have to click on a button to reply and/or get full context.
If the thread messages' background color are all the same we don't have to open it to get full context, we can see it in the chat at a glance.
And once the thread goes off-screen the color becomes available again for a new thread.
Sounds like a good idea to me!