Changing hair colors on your own may be scary, but it's not impossible!
To change hair colors you'll need to first determine if the color you want is darker or lighter than your current color.
If it's darker - great! All you need to do is pick your dye type and color.
If it's lighter or a fashion color (pink, blue, etc) - also great! You will need to lighten your hair using bleach.
There are three types of hair dye; Semi- Permanent, Demi-Permanent and Permanent.
Semi-Permanent colors are essentally a stain for the hair. Not used with developer, the process does not lift the cuticle, but rather clings to that layer. These colors can last anywhere from 1 to 2 weeks, depending on the level the hair is at the time of application. Colors can range from natural (black, dark brown, etc) to fashion (pink, blue, etc.) When trying to acheive a fashion color, you may need to lighten your hair prior to color application to acheive the vibrancy you would like. It is possible to put Semi-Permanent dye onto darker hair, but the outcome is usually more of a hue added on top of the pre-existing color.
Demi- Permanent color is a a halfway point between Semi & Permanent color. Used with a special peroxide - usually called "demi developer" or simply a 6 vol developer - the cuticle is lifted slightly, depositing the color a bit more thouroghly. These dyes typically last 2-3 weeks. Similar to fashion colors, you may need to lighten your hair for your desired outcome.
Permanent Hair dyes are a valuable option for many. Typically used with a 10 vol developer, this product significantly lifts the cuticle of the hair, lifts the color of the cortex a level and deposits color on the cortex of the hair. Due to this process, these colors typically last a month or longer.
Gray hair acts almost like coarse hair, and therefore needs stronger processes to be covered. Permanent colors are an option, as well as a few special formulated rinses and semi permanent colors.
There are a few dyes on the market known as "lift and deposit" colors, which does exactly as the name suggests. Using 30 volume developer makes this process possible. Formulated for darker hair, these products will lift the cuticle of the hair and proceed to lift the color of the cortex approxiamtely 3 levels, then deposit the desired color. Think of it as combining the steps of bleaching and then dying your hair in one. Theoretically, you could mix 30 vol with a Permanent color for a similar result, but I personally have had the best luck with brands that are specifically lift & deposit.
The mixing ratio refers to the amount of developer mixed with the hair color. It will typically appear written as "1:1" which translates to 1 oz of product to 1 oz. (Say your hair color was 4 oz, you would need 4 oz of developer.) The typical ratio for permanent color will be one part color, one part developer. Adding double the amount of developer will cause the color itself to lighten. It will vary by brand, and to figure out the recommended ratio look on the box for the brand's instructions.
At the store colors will be numbered 1 - 10, referring to the levels mentioned earlier. After you decide what shade you'd like, you'll notice there colors usually have a letter following the number. This is referring to the undertones of the haircolor, and can help you be more specific with shades. For warmer shades, look for "G" for Golden or "R" for Red. For cooler shades, look at "N" for Nuetral, "V" for Violet, "B" for Blue or "A" for Ash.
When applying an all over color, there is no right or wrong way to color your hair. To ensure an even saturation, I recommend following the sectioning mentioned earlier, applying color to all the roots first following that method and then apply the rest of the color to your sections. You'll want a non-metallic bowl, an applicator brush, clips and gloves. Happy Painting!