Can't Use Black Colour With Paintbrush Tool

Hello I am using Photoshop Elements 2021 and use the paintbrush tool to change the colour of the background on my photos. The colour I use is black but for some reason the paintbrush tool will not use the black colour. I can use any other colour I want but not black. I have been using the pencil tool as a workaround but do not understand why the paintbrush will not work. Any advice will be greatly appreciated.