Check out the polycount wiki and read up on shaders and textures. I suspect you are confusing some terms -- very understandable because the meaning of the technical terms isn't exactly the same as their ordinary usage. Looks like your question is already answered, but I'll add just for reiteration : yes, absolutely you can…
It is possible if the shader you are using is set up to allow it. Varies per software. Examples: Maya - diffuse texture automatically overrides diffuse color value. 3ds Max - diffuse texture automatically overrides diffuse color value, but there is also a map % parameter for every texture channel available by default, so…