Why is my video purple? (a.k.a. the smurf effect)
Not sure. But many people have fixed this problem by changing their video output module.
Go to Preferences -> Video -> Output modules, and set Video output module to something different, like DirectX video output.
Be sure you have advanced options enabled to be able to access this option.
Also, you might need to disable the "YUV -> RGB" checkbox in DirectX section of Preferences -> Video -> Output modules.