Image display is yellow

Your projector, when working correctly, probably sends thousands of red, green, and blue dots or rectangles of varying luminosity to the screen. A group of three dots of appropriate luminosity will add up to a grey or white dot. Red and green without blue will add up to yellow. So for some reason apparently your projector is not projecting any blue. If you're lucky it won't be the projector at fault, but instead, a loose or defective cable.

I have the same issue, and I have found that the LCD appears to be going bad. I came to ifixit looking to see if anyone has done an LCD replacement, but unfortunatly there are no guides. This is for my office, so we may just upgrade since it is quite old. However, for the ammount of time that we use it, I would say that this LCD did not last long.