One of the first things you'll have to decide when considering hair color ideas is the results you want. Based on that, you can figure out what type of hair dye to use.
To start, there is permanent dye. The advantage of permanent dye is that it gives you 100% coverage and will take care of the nasty grays. It is also the only way to lighten you hair if you have dark hair. The other types of hair dyes can only darken your hair.
If you're considering dramatic hair color ideas, you'll need to use a permanent dye - especially if your hair is dark. The most common method is a "2 step process" that removes color in the first step and deposits the new color in the second step. The first step completely removes the natural (or previously dyed) color so the hair is white or very light blonde. The second step then deposits an entirely new color into the hair to get the desired results.
Since permanent color gives you 100% color, this is also the best option for creative hair color ideas or the most dramatic change. If you want purple hair, this is the way to go.
The bad news is that is that stripping your color can leave your hair dry and damaged. You'll want to use a shampoo and conditioner for color treated hair or something with extra moisture.
In addition, with permanent color, you'll have the problem of roots showing after about 6-8 weeks. If you're working with your natural color to cover grays, there won't be as much contrast between your roots unless you're really gray. You may be able to stretch more than a month before touch-ups are needed. Major changes are going to require major maintenance unless you don't mind your roots showing. This leads me to another downside of permanent hair color - if you don't like it, you have to grow it out or re-color it with another round of permanent dye/color remover.
Very important - since permanent hair color is such a commitment and involves a chemical process, it should ideally be done by a professional. Otherwise you could literally fry your hair with the chemicals. If you do decide to try this on your own, make sure you use a "single step" process and you really understand the how it needs to work. The original color is removed and the new color is added in one step making this easier for a novice.
If you're just starting to explore hair color ideas, permanent color may not be for you unless you're really sure about what you want to do.
