I had this same problem. Suddenly the color in my fcp sequence became orange and darker. The original files outside of fcp look normal. Also, when I had two video channels going, and adjusted the color, the orange and darkness went away, along with the render. When I rendered again the orange and darkness came back. I took the entire sequence and copied it into another project sequence. This seemed to fix the problem. When I went back to the original sequence the color issue was fixed also. Really weird stuff, but I fixed the problem.