I've black hair and I want 2 subtly lighten 2 dark brown hair w/o my mom knowing. What should I do?

I also have black hair and the only way to lighten it is to lift the natural color with bleach (hair bleach) I cannot stress enough the importance of going to a professional hair supply store to get these products. Box dye is a big no-no. You will need a 40 lightener and also a toner. When you bleach the hair it is naturally going to turn a shade of orange, that is where the toner comes in. The toner will help take the brassiness out of your hair. After you do that you can proceed with whatever shade of brown you prefer, but I suggest an "ash brown" to help make sure no residual orange/red tones pull through. Ask the worker at the store to help you as it is important to make sure you purchase the right items. Good Luck!