import all texture without alpha to gta3.txt in TxD, select Overwrite, and uncheck everything else.
for the pizzaboy scouter bike to look like the screenshot change the color data in:
carcol.dat

color for pizzaboy:
pizzaboy,7,3

I do everything I can with the recourses I have, sorry if the Mod isn't that fancy, I'm doing these Mods on my phone...it's a Moto G 6 plus very slow compared to a computer.