Simple brick multishader

For more than 6 hours I've been hitting a brick wall so to say in trying to make a simple brick wall multishader. At this stage all I want is to tile a main brick texture, then in certain parts have a different brick show on top of it. I've done this (and very easily) in a number of other programs over the years but I am baffled when it comes to getting it to shade my wall in A3. The MC covers the brick completely and there seems to be no point in my using the _CO textures (which are important in this case). Can someone help? My mask seems to have no effect at all.

I'm not interested in using an MC map though it seems to be a necessary evil. All I want are my bricks to show, is there a way to have an MC that has little or no effect and allows the brick colors to show?

My real goal is to have

2 similar brick tiles mixed to break up the sameness

overlaid in select areas with a third distinct and different colored brick

with dirt in places overall

Anyone have a simple example of a multishader that does that?

Solved after an accidental discovery.

I had a texture in the selection in Oxygen, when there should only have been the rvmat. Removed the texture, my brick looks great now.