Customising hair dye to create a signature colour for your tresses isn't a difficult endeavour, when you use the same brand of over-the-counter colourants. This gives you the ability to make-up shades that aren't normally sold commercially, which gives you an edge in having your own signature look. Knowing how to mix two different shades of over-the-counter hair dye only requires a little extra work when mixing and applying to your hair.
Open each over-the-counter box of hair colour and remove the contents from the box. The standard contents of each box are the colourant, the developer, gloves and sometimes a pack of conditioner.
Separate the items from the two boxes and group them together. For example, put the two bottles of colourant together and the two bottles of developer together.
Most over-the-counter brands contain enough colour and developer to make a 113gr. application of hair dye. However, some boxes are bigger than this, so you may need to use an applicator between 340 and 567gr, depending on your needs.
Pour the two containers of developer into the applicator bottle. Pour the two bottles of colourant into the bottle with the developer. Secure the cap and shake continuously for two whole minutes. This will disperse the colourant with the developer, making it ready to use on your hair.
Use the same brand of hair colour so you the formula stays the same. Mixing different brands may have adverse effects. Use a deep moisturising conditioner after rinsing the hair dye from your hair. Most over-the-counter hair dyes come with tubes of conditioner for this purpose. Have your hair trimmed after dying, to further prevent breakage, due to the drying that hair colouring causes.
Only colour your hair in a well-ventilated area. The ammonia and similar chemicals in hair dye are noxious and may mess with your breathing if you apply it in a closed in area.