Hair dying is great if you just want to try a specific color for a short while. Hair dye will vanish after you wash your hair x number of times. There are two big groups of hair dye: Regular hair dye that vanishes after your hair has been washed about four times and semi-permanent hair dye that is supposed to go away after eight to twelve washes but that sometimes lasts longer than permanent hair color. The latter can even have a slight bleaching effect.
Lindsay Lohan, natural redhead.
The lighter your natural hair color, the easier it is to get a significant effect by dying your hair, obviously. However, like I mentioned earlier there are semi-permanent hair dying products that do contain small amounts of bleaching. A great tip is to dye your hair first to see what the color looks like on you and then proceed to color your hair when the dye wears off. A fun thing about hair dye is that you can try a color that will look unnatural on you just to see how it looks. If you're not happy with it, your mistake will only be visible for a couple of weeks, maybe even less. I would recommend regular hair dye for this purpose though and not the semi-permanent type - just in case.