Here is an example following your 10 second tip tutorial.
So I created a mix map with a FP color map in the first slot, and a red color on the second slot.
Note that there is only one orange texture attached to the FP color map.
It works fine. Until I decide to add texture wihich is NOT DEFAULT to the FP color map, and the red color of the mix map disappears.
The problem is connected to the texture though. Because I can add a color tint to my FColor map without problem. The red is still there.