You're in Quick Mask mode. Press Q to get back to normal mode.
Thanks, but my brush is not working now, I've reset the tool but still not working.
The subject of your thread has already been marked as answered and is now just for reference.
The brush is a different matter and you should post a new topic. Adding a different problem to an already answered one just clutters the thread.
I would suggest taking a full screenshot of your Photoshop workspace with the layers panel open while you describe what you were doing in your new post. "Brush not properly working" would be a simple yet descriptive subject line. Also mention the model tablet you are using as well as your OS (Windows or Mac version).
Try disabling Quick Mask, press Q on the keyboard