Use The Overlay Modes To Check Your Lightroom Masks
Lightroom masking is powerful and helps photographers emphasize subjects and craft stronger images. The mask overlay defaults to a red color showing an area the is mask. Depending on your photo, that red overlay may be difficult to see. There are three other color overlays for masks in Lightroom - green, white, and black. Cycle through these using the keyboard shortcut Shift-O to double check the precision of your mask.
See this technique in action in the short video with this article.
You Might Also Enjoy These Lightroom Posts
Precision Edits Using Intersects In Lightroom