Kilz Primers are usually very high quality. As such, it’s most likely to turn yellow when we make some sort of error in using it.
When Kilz primers go yellow, it usually has to do with the surface you’re applying it to. This could be the severity of any stains you’re trying to cover up, the type of paint you’re covering, or the dirtiness of the surface.
Covering latex paint is different from covering oil-based paint. Covering lighter colors like white paint will be different from covering darker colors. Dirt and other debris can alter the color of primer products.
Note all these possibilities as you read through the following post, which will provide more guidance about why primers adopt a yellow tint.

Why Is My Kilz Primer Turning Yellow?
When you think your Kilz Primer is turning yellow, the most likely explanation is that you need to apply more coats of paint primer to cover up stains more thoroughly. A single coat may not be enough.
The most common complaint registered by Kilz Primer consumers, especially if they have purchased a water-based primer, is that multiple coats are required to get the job done.
The most common feature of a water-based Kilz primer is that its design is intended to seal porous surfaces, primarily associated with freshly completed drywall.
Sometimes, a water-based Kilz primer will also be designed to promote adhesion during your subsequent paint job. But that is usually as comprehensive as it will get.
If you are lucky, a water-based Kilz primer will conceal minor damage to the surface you plan on painting over and also sometimes covers previous colors.
Some water-based Kilz Primers will also produce a mildew-resistant finish, which can prevent stains from mold and mildew.
However, if you want to deal effectively with massive yellow stains on your wall that bleed through the primer, you will need to take more drastic steps.
You can do this either by applying many more primer coats or by purchasing an oil-based primer, which can better cover stains due to its thicker consistency.
Things That Make Kilz Primer Look Yellow

Your Kilz Primer will mostly look yellow because your wall has gone yellow, or the previously used color on the wall was, in fact, yellow. But several other factors can affect the tint of your primer, such as:
Using Kilz Primer Over Oil-Based Paintwork
The great tragedy with oil-based paints is that they do yellow over time, whether from heavy sunlight, no sunlight, or exposure to mineral turpentine. In fact, turpentine can cause the primer to go brown.
You may need to double up if you apply the primer over an already yellowed coat.
Water Leaks
There are two things to note about water leaks on any surface. The first is that those leaks usually go undetected for a very long time, which means that you could apply your Kilz Primer without realizing there is a leak, only to find that out later when a yellowish water stain emerges.
The second issue with water leaks is that they cause moisture levels on the surface to rise. Both of those things contribute to yellowing on your painted surfaces.
The Primer Has Hardened And Cracked
If you have not prepared your surface correctly, the primer can crack. These fissures let in moisture and stains associated with yellowing on your surfaces.
Previous Surface Color Was Yellow
People often underestimate the extent to which yellow can bleed through a coat of primer because it is neither the brightest nor darkest of colors on the paint chart.
You Let Your Animals In The House
Animal urine stains are an absolute nightmare to remove. If you’re trying to cover both the color and the stench, you may need to paint more aggressively.
There Is A Lot Of Smoke And Grease On the Surface
This is usually a problem for surfaces in a home where people smoke indoors, cook greasy meals, or have a fireplace with access inside the house.
How Do You Keep Kilz Primer From Turning Yellow?

Beyond trying to avoid all of the potential mistakes we have mentioned above, you could save yourself a lot of headaches by using more water-based paints in your home instead of oil-based ones. Water-based paints are easier to cover up.
How Do You Whiten a Yellowed Kilz Primer?
The simplest solution will be to use more robust Kilz Primer products, especially primers that are able to deal effectively with mold and mildew issues.
Conclusion
Primers often yellow because of previous stains, water leaks, or debris. For previous stains, you just need to apply more coats. Water leaks are a little more intensive, needing you to treat the source of the leak. But you can simply clean up dirt and debris before priming.