My panasonic hdtv seems to have developed a yellowish tint to the screen

Sounds like the polarizing film is burnt on one of the three colored lenses that are located next to the projector itself. In order to fix this this it is necessary to remove the ballast and projector units, then disassemble the projector housing to expose the lenses. there are green, blue and vermillion (reddish) lenses. the vermillion lense is the one that causes the yellow tint after it has been damaged.
searching for the pt-43lc14-k service manual (the 'k' version is the more complete one) will provide you with daigrams and such.
I am currently undergoing this repair myself, thus far we have disassembled the television and are waiting on new vermillion polarizing film in order to complete the reapir. Good Luck, it isn't too difficult. Just take lots of digital camera pics (for screw location and sizing) and you should be fine.