My natural hair color isn't light, but I did bleach the portion of my hair that I dyed blue. But even when I dyed my natural color blue, it didn't fade to green... more of a teal. I have medium brown hair, it's not dark but it's not light.^^It might be because your natural hair color is so light, I know that the dye takes better to really light hair. I just put the blue on over my hair when it was brown. I got a beautiful deep sapphire shade as a result...but it also faded quickly to green. I don't know for sure if that's the case, but it may well be since they always tell you to bleach your hair to get the best color result.