Hi! Just started with ZBrush, and I need help. For some strange reason I can’t see my mask selection. It’s working, but invisible. Here’s how it looks like: https://youtu.be/g9HlfcgWQDA
Since support saying that it’s not their business, I’ll appreciate any help. Thank you.
Welcome to ZBC. 
You have the BumpViewer Material selected. This is a special material and shouldn’t be used while sculpting. (It converts any grayscale color on the model to a bump effect.) Switch to another material and you’ll be able to see your mask.
[I moved your post to the [Other Questions & Troubleshooting forum](http://www.zbrushcentral.com/forumdisplay.php?101-Other-Questions-And-Troubleshooting-Forum) - the best place for questions like this.]