Here's an example of a test I did trying to add new FC Barcelona "streetwear" to the game:
This is the streetwear:
This is how it looks ingame:
It is possible, but like I said, it's very difficult to make specific colorways, because the game will try to recolour the textures to the kitcolors that are set in the database.
So for example if I want to add blue/red streetwear to Barcelona's home kit, this will generally work well because those are the 2 colours for Barcelona's home kit in the database. But if I also want to add yellow streatwear to Barcelona's home kit, the game will attempt to recolour them to the values in the database (red/blue), this makes it difficult to have colour variations like in real life.
For example, in real life Barca have multiple variations as "home" streetwear, that feature different colours. A lot are of course blue/red, but there are also some in grey/light blue or black or even yellow. For those variations I need to find out how we can make the game read different colours and ignore the database values.