They might be satsuki azaleas. They are a Japanese azalea family that was bred for this highly variable flowering. They typically have flowers with all combinations of colors, for example pink, white, and white and pink, sort of like you get when you breed different colored cats.

If it is not a satsuki, then you are seeing the effect of light on the color. There are two effects that I am aware of.

One is the light triggering of some pigmentation. Certain colors are more prominent in flowers on parts of the plant that get sunlight, direct or indirect.

The other is fading, in which colors fade with time in flowers on sides of the plant that get more sunlight, direct or indirect.

Based on appearance of the blooms, some of my Azaleas have some blood from satsuki. That might be the cause of the problem. I also agree that temperature and light are factors.