Paint Layer in Fill not using correct color

Hey there,

I've got a question/bug i've run into. I often like to make fill layers ( and paint a mask ), and then add separate paint layers inside of that fill to get better color variation inside one " layer"

For some reason halfway through my project the pain layer added to any fill layer is a desaturated green. Making new layers, changing color, etc etc does not resolve. 

Does anyone know why this would happen? More importantly, how to fix it? Image attached and thanks!