Make sure the input signal setting on the Signal menu matches the signal from the connected device. See Adjusting Signal Settings.
If the image is too purple and you’ve connected a computer or RGB video device to the Computer1 or Computer2 port, select RGB as the input source. If you’ve connected a component video device to one of these ports, select Component.
If you’re projecting from a composite video or S-Video source, make sure the correct Video Signal is selected on the Signal menu.
Check your computer display settings to correct the color balance.