Nice list of bugs and requests you've got here. Some of them are puzzling though...
Car colours should never desync since all colour data comes from the server on spawn then gets updated as it changes. Have you experienced this randomly or when working with a script?
Setting player health to 0 causing a crash makes no sense at all. The method which does this is the exact same method that the server uses to set the health. This will need to be looked at more thoroughly but without debugging it doesn't make sense
WeaponAmmo not updating on the server
is a bit of laziness on our part but it should update for the client. We'll look into fixing this.
Colour class returning only the R value... I implemented a fix for this months ago but it must have got removed in one of the many code reverts that happened. A tester should have picked up on this.
Custom weapon.dat, I'm pretty sure this used to work and we haven't touched this code for a long time so it's strange how it doesn't work any more (unless it never did, but why did the testers not tell us?!)
Modded cars causing a crash, this is due to collision tests in GTA itself. If a car is modded so that it runs lower or is smaller than the original model then on remote player's screens, the original model will be inside other objects. This likes to make the renderware engine cry if too many points are intersecting which causes the crash. It's the same reason that spawning 50 cars within each other crashes. We have looked into a sort of fix for this crash but we haven't got around to implementing it yet. People should just stop using modded cars...
As for the tab crash when pressing T and Tab, tab autocomplete has had so many issues since the original implementation and could do with being rewrote. I'll prod AdTec to fix his code (since he wrote that part)
With the feature suggestions, we will look into these when we get time