The natural hair color depends on the pigment called melanin. Melanin determines how intensive and vivid the hair color will be. Other pigments which are eumelanin and pheomelanin determines what shade your natural strands will have. For example, round granules of pheomelanin make hair red and golden. Elongated eumelanin granules make up dark and brown hair colors.
If there is a lot of pheomelanin, then your hair is brown and black. In case if there is just a little of this pigment, your hair becomes ashy and gray. The more eumelanin there is in your hair, the more vivid red and golden shades will be.
If you want to dye your hair, it’s important to consider its natural color and peculiarities of different pigments. Each hair color has its own tone level. It’s important to find it out and correlate it with the tone level of the hair dye you want to use. The main rule that you shouldn’t dye your hair using the hair dye the tone level of which is darker than the original shade of the strands.
It’s also pretty dangerous to dye bleached hair in any darker shade. You will have to do repigmentation in order to bring back your original hair pigment. Of course, if you don’t want to have greenish strands!