FAQ: What Happens If I Mix Two Different Colors

Question:
I would like to mix a semi-permanent color with a demi-permanent color. Both colors have similar shade. Can I do it?

Answer:
Yes and No.

• No, you should not do it, if it involves TWO different companies. Once I run out of a developer (peroxide) of one company and I mixed a developer of a different company with a permanent color. But my mixture became very watery by a body heat and was constantly dripping into my clients face as the hair was processing. I had to have an assistant to stand there and wipe and wipe and wipe.... it was a mess. However, the color came out beautiful. What happened? The chemical reaction of a developer and a color was supposed to "emulsify" no matter what. It would not "run" under any circumstances if I would use both products from same company. But this particular company made sure that colorists always buy their compatible products - this way they ensured higher profits. However, some other companies do not design their color and developer that way and if a colorist runs out of a developer, he/she can use a different one... That said we can move on why "Yes".
• Yes, you may try it, if you work with a product of the same company. Here is what can happen? 
  Chemical-wise: your demi will become "demi-semi" and semi will become "semi-demi" - in other words you will strengthen semi-permanent color (it will last longer), but weaken demi-permanent color (it will last lesser time).
  Color-wise: if you mix two "very similar pigments" and they intermingle, then they become slightly different from what each original would be. But, if you mix two different colors, then you should look at a color wheel and see, what would become of your color if you mix colors of different shades.

Note: 

This post should be taken as a first step for a discussion with your hairdresser and/or colorist about your ideas, desires or problems with your hair. Under no circumstances, you should act upon this post ONLY. I strongly advice you to have your hair done by a skilled and reputable hairdresser/colorist in your area.