Color toner is used up when printing primarily black and white

[emilymess]

I have a MF743Cdw and my color toner is running out even though I rarely use color when printing. I have the "Color Mode" set to "Black and White", I don't see any other settings to change. I really don't want to change the color toner as often as the black if possible. 

[shadowsports]

Black is a by product of primary and/or seciondary colors.Setting printing to "Black and White" only stil uses some color toner.  

[emilymess]

I understand that, what I don't understand is why is there a black toner cartridge if the machine is going to use the color cartridges to print black anyway? Why bother? I want to know if I can change any setting so that it uses only the black catridge like a monochrome printer.