My photoshop is Black and white. I can paste a picture from a Image sit, and it could be in color.. It applies in B/W. I use a blue brush, its greyish-black. Something may have happened when using my tablet, im not sure.
Most likely you have your mode is to black and white. Just change it back to RBG. or Image > Mode > Grayscale is checked; just change it to RGB or something.
No problem. Yeah, it randomly happens to me.. Like I'll copy and paste a B&W picture into an RGB document and it will automatically change it to Grayscale; and for whatever reason it will stay like that.