I have a Texture with 6 channels. Each channel store a mask that is used to change a color of a part of my player's sprite.
When the texture only had 3 channels it was easy to implement this color change using a shader, but the only way I can think of how to do it with 6 channels is using 2 textures (which seems pretty annoying to me).
It's possible to use a 6 channel texture nativity in GLSL?
Using multiple textures is the standard way this is done, and GPUs are well adapted to that use. We store all sorts of things in textures, not just colours and masks.
That doesn't mean you have to work with multiple textures, of course. If it makes sense to you, just add some middle-ware that converts the multi-channelled texture into an appropriate set of textures, so you can author the textures in a way that's convenient for you. Though again, the tooling also tends to work with one- or four-channel textures for the most part.
The maximum for a single texture is four channels in every GPU rendering API that I know.
While it's technically possible to encode more data into those four channels (e.g. storing eight 4-bit values, instead of four 8-bit values), you'll run into two main problems with that:
Using two textures is probably your best solution here.
