If I recall, joint textures used to only cover a certain level of transparency on the joints meaning you could use a joint color and it would haze through it somewhat. But I have no idea if that is the same now as it was back then. Either way, now you can choose to have joint colors (given you can't afford joint textures) or you can use joint textures. So there isn't really a need for someone to use both but I mean if they wanted to, no one is going to stop them. 
joints have textures when u buy joint textures but laxes / forces is the joints color
when u buy and use both then u have textures on your joints + color too
when u buy and use both then u have textures on your joints + color too
