How can I get my HP printer to print in black and white only even when one of my color cartridges is out?

I use a Mac to print with my printer and for whatever reason just because my Magneta cartridge is out it won't let me print in black and white by just using the black cartridge which is full. Does anyone know any way around this? I read online that this is a marketing strategy used to get more people to buy colored ink even when they don't need it and could just use black ink.