My screen is flickering purple and cyan
Sorry to say that looks an awful lot like a hardware error.

It could be a bad video card, issues with the screen itself or the connection between the two (cables, connectors, etc.).

If you boot into recovery mode is the issue still present? That would rule out an issue with your OS if it is still there.

My advice, seek the help of a qualified Apple tech. Either at an Apple store or a good 3rd-party Apple certified repair center.