masked area changing to a color

[sbradom]

Suddenly, when I use the brush tool to create a mask on a black-and-white image, and then adjust the exposure slider the masked area, turns to a color instead of just adjusting the brightness. It used to just adjust the brightness, but something has changed and I don't know what. I need help to fix this. 

[Per Berntsen]

Please post a screenshot of the entire LrC window at the point where the issue occurs.

Do not attach the screenshot, use the Insert Photos button in the toolbar to embed in your post.

[Jao vdL]

The overlay is probably turned on. Try hitting the "O" button on your keyboard once. The overlay should disappear.

[sbradom]

The correct answer is the my preferencces werre corrupt. I trashed them and that fixed the problem.