Brush shows red, not changes, when painting

Hoping this is a simple rookie mistake:

As long as I've been using Lightroom, when I use the brush tool to edit parts of the photo, the changes to the image appear in real time when I'm painting. Not sure what I did today, but all of a sudden instead of showing the changes it shows the red "mask" (for lack of a better word) instead of the changes. Previously the only time I saw this red mask was when I hovered my mouse over the blue dot showing that particular Brush. I want to go back to how it was before, with the Brush showing the actual changes in real time - how do I do this? I have Lightroom v. 4.4 and use a PC if that helps.

Any insight would be greatly appreciated!