Make sure the input signal setting on the Signal menu matches the signal from the connected device. See Adjusting the Input Signal.
If the image is too purple and you've connected a computer or RGB video device to the Computer1 or Computer2 port, select Computer as the input source. If you've connected a component video device to one of these ports, select Component Video.
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.