I don't think the auto-installer has anything to do with interior colors unless it's forcefully installing a set interior texture, IIRC it's what you do to the model in ZModeler that dictates the ability to choose interior colors ingame.
Maybe since Zoqqer has quit TDU-1 modding, he should tell you how it's done instead of following a certain other modder's precedent and keeping all the secrets to himself.
The more info gets shared, the more modding advances. The more secrets get kept, the more modding is deliberately gimped.
Just an FYI, TDU-2 is dead before it ever got started Zoqqer, the game is bombing bigtime with only 20,000 copies of the PC version sold world wide. You're wasting your time waiting for TDU-2 to be hacked and moddable. By the time it ever happens, you could release a ton more cars for TDU-1.
You do realize that the mod still works perfectly if you do a manual install right??? The spoiler still works, the interior colors still work, there's no reason NOT to do a manual install unless you're so lazy that you don't feel like setting your own cams and physics.
Not everybody likes auto-installers, and not everybody likes the cars chosen to be overwritten, and in many cases, the auto-installers have caused more game crashing than manual installing ever did or ever will.