Questions about semi permanent hair dye?

I'm thinking about coloring my hair with semi permanent dye, but I've never done it before so I'm a bit nervous. My hair is light brownish, but I want to change it to a darker brown. Nothing really dark; just brunette. I also want to add a blue streak. How long does semi permanent dye usually last? Are the roots terribly noticeable when your hair is growing out? Would I have to bleach my hair in order for the blue streak to come out, because if I did, wouldn't I have a blonde streak once the blue faded away?

Questions about semi permanent hair dye?

Semi-permanent hair dye lasts about 8 weeks and fades out gradually. If you don't do a color that is drastically different from your natural color, it shouldn't be too noticable as your roots grow out.

As for doing a blue streak, if you don't want that to be permanent, you might want to visit your local costume or stage make-up store. You can get hair color that you can streak into your hair for an evening and then wash right out the next morning. You might want to try that before you use any sort of semi-permanent color for the blue streak. That way, you can experiment and not get stuck with something you don't like.