You have to buy a semi, demi or permanent.
If you buy a semi-permanent dye, it will wash out in 6-12 shampoos.
If you buy a demi-permanent dye, it will last longer, about 24-30 shampoos.
If you buy a permanent dye, it cannot be washed out and it has to grow out.
If I were you, I'd buy the semi, see if you like it, if you don't, just be patient for a week or two and it will wash out.
If you do like it, go to the store will your semi permanent box and look for the same color, then buy the demi.
Permanent hair color contains ammonia and peroxide, which can damage hair, if I were you, I'd just stick to the first two.
Good luck mate!