Question on using lemon juice on dyed hair...?

Not too long ago, I had died my hair reddish. If you look up Allison from American idol, my hair is like that, only not as bright. Since I had only died my hair two days ago, I don't have roots. I did my hair myself, because the salon I go to said that if they dyed my hair reddish they would have to dye it twice, because I had 4inch roots. They would have to do it twice because if they did it once, only my roots would show the color completely. I decided to do it myself and I've only dyed it once so far. What would happen if I put lemon juice in my hair and laid out in the sun? Thanks!