If this is your first time experimenting at home with hair dye colors, I would suggest that you try it out with semi-permanent hair dye that washes out in about 8-10 washings with shampoo, rather than going straight away for permanent hair dye. Of course, your professional hair stylist would be able to advise you on the colors and highlights that would suit your style (and even your job!), but if you are going to do this the D-I-Y method, it is essential for you to have a basic understanding and knowledge of how hair coloring works.
The most important is to understand the different types of hair dyes available and how the colors react to the natural pigments that is already present in your hair. Otherwise, it is very likely to end in disappointment when you find that the end result is not what you anticipated or wanted. Repeated experiments could lead to damaged hair. For example, if you have dark brown hair, and would like to color it light blond, you have to know that it cannot be done with semi-permanent dyes. Semi-permanent color cannot lighten the hair. This is because it does not contain peroxide or ammonia, or even if some brands do, it is in very low levels. It does not strip your hair of its natural pigmentation and therefore, if the original pigment is dark, the lighter color would not fully show through.
This means that for a head that has dark and gray hair, semi-permanent dye is not suitable for use, as it is not able to make the dark strands and the light strands to become the same shade and color. The final color of each strand varies according to its thickness, original color and ability to absorb the color pigments. The white and gray strands would still be very visible in contrast to the dark strands, as semi-permanent dye does not lighten hair. However, it would still be acceptable for originally blond hair with gray/white strands as the contrast is minor and they would be able to blend in with the rest of the hair.
Many people like the effects of semi-permanent dye as the final effect is often a soft and subtle spectrum of shade variations across the whole head, giving the appearance of beautiful glowing natural highlights. And, the absence of peroxide or ammonia in the hair dye makes it ideal for damaged, fragile or fine hair, as it is safer and more gentle on the hair than permanent dye.