My tv screen when on turns yellow then after a while it will switch back to normal colors what can be wrong with it....

Televisions covered: all Projection with yellow picture, but not Projection TVs with a yellowish tint surrounding objects in a nearly normal picture.

Yellow = red + green
normal picture = red + blue + green (RGB). See illustration.



Fig. 1 Additive color mixing in an RGB monitor, or RGB Projection TV.

The circuitry powering your blue output, or the blue light engine itself is starting to fail.

Operating Theory:

The lamp module shines a bright light into the optical unit; there are a series of lens and baffles, and at the top of the light engine, a lens puts the picture into a mirror which is reflected onto the screen; All video and color is processed thru the light engine. Blue most commonly fails first, leaving a yellow picture.