How to Color Hair Using Demi-Permanent or Deposit-Only Color

You don't need permanent lifting color for all your clients. Unfortunately, colorists have been confused by the names companies call their products. For example; Why do you use developer with demi-permanent color. If the product is not supposed to lighten the hair and the dyes are demi-permanent, what's the function of the developer?
I'll explain the differences between them and explain why one is better than the other in different circumstances. I'll show color formulas and combinations on bleached hair, white hair, brown hair, and 50/50 gray.