I wonder why you use only GameMaker Studios. Sure, it's free but Unity is free too. But then in Unity not all feautures are there in the free version, so why only GameMaker?
I like Minecraft for only 2 reasons.BIG worlds and mods. Why I don't like it? Because survival games. I just can't play on a server like hypixel and don't get pummelled on/rage quit.
Let me guess: Go through a image editor take the skins color and put it in the rig's texture.
I think you could try making some preset colors in the rig's texture file. That could make it easier.
Also this is very good. Nice job!
EDIT: I actually tried it out and...it was purple...So...um...that.