Diffuse color does not affect the texture used in diffuse slot.
Diffuse level does affect the texture.
If you are using some diffuse color (e.g. red) and a texture, and you scroll down to the list of textures in the material editor ("Maps" rollout) and you lower the "Amount" for diffuse, this will blend between the diffuse texture and the diffuse color. So if you change it from 100 to 50, this will show 50% of your texture and 50% of red-ness. This is the default behavior in 3ds Max (AFAIK).