FCPX - Blue or Green Screen Editing color issues

I have been having problems with my blue screen editing in final cut pro X. I have a blue backdrop and when I want to edit it in the program all goes fine but I when I edit my blue screen (following the tutorials that I found online on youtube for final cut pro X) the colors on my main image get ashier or washed out totally.

For example, when I used a blue screen and I use pink, purple shades they become gray or unoticable (depends on the hue) and skin tones become ashy or ashy with a green hue.

Am I doing something wrong? or is this a glitch?