From past experience I'm not so sure that they can't see red light and I've heard others say the same.
If you want to use a bulb then I reckon the main thing, whatever the colour, is that the colour is quite deep - eg. with a red bulb, the bulb itself should look red when in use, and not pink.
Some coloured spotlights have areas of clear glass around the stem which totally defeats the object, so double check any spot lamps before buying.