My tv sceen has a stain that makes anything white look yellow.
The color image is comprised of three colors, Red, Green, and Blue.
All the other colors are mixtures of those colors. The yellow picture indicates that your set is lacking sufficient blue drive.
First of all check to make sure that the tint control is not misadjusted.
The next thing is dependent upon the age of your television. If it's an older set that yellow tint is a sign of an aging picture tube.
If it's a newer set, less than 5 years old, have it analyzed by a electronics technician that is familiar with televisions if he is skilled enough he will know right away if it's the picture tube or not.