I see what you mean, I just tried pointing a laser level at my monitors, it was visible, but not very clear at all. To be honest I don't see that using a different coloured laser would make any difference - red, green and blue is what is makes up the display of an LCD, so I would expect them to all be absorbed easily. Really I don't think any sort of light pointer will work very well, I think you'll have to resort to an old-fashioned pointing stick.