Masking problems driving me mad!

[audacity10]

Hi, I'm being driving crazy trying to disable a mask from my tool in Zbrush without any success. I've Ctrl/Alt dragged to remove it, then when I Ctrl Click outside, it reappears. I'm pretty new to the program so I'm a bit dipsy with the controls at the moment.

I've noticed the model is darker than usual and if I change my brush etc, it goes even darker - so I'm wondering if something has been applied unintentionally? The problem exists even if I reload Zbrush...