That's not a layer mask. That's a normal pixel layer clipped to the underlying pixel layer.
Add a layer mask by clicking the mask icon in the Layers panel. It will appear as an additional thumbnail beside the pixel thumbnail. A mask is always black and white. Black areas hide the pixel content, white reveals.
I'm sorry but i think i confused "Layer Mask", with "Clip Mask Layer" i don't want a Layer mask i want a clip masl layer above my painting so i can only paint over a certain area and not the background. But whener i add it my colors will change.