Using white medium as part of the “priming” process is not unusual. I tint mine with dry pigment from Gamblin using an equal amount of zinc and titanium white. It produces a very nice neutral white which covers my birch panels well, providing an excellent base.
However, I started to build relief in my paintings using the same medium and it began to get thick, tacky, and difficult to use. Additionally, the color would change after being on the heat for longer than an hour or so. It turned yellowish and thus turned the color I added on top of it yellowish as well.
It was very frustrating and I realized I needed to solve the problem. The solution was R&F white encaustic paint. It takes little to tint my normal medium (R&F as well) and it doesn’t change texture or color, even after several hours of heat.