The air is hazy, and the sun is red. And the sunsets? The sunsets are vibrant. Why?
It is for the same reason a sunset is red. Particles in our atmosphere scatter light, and they scatter blue light more than red. At sunset, the sun reaches us through more of the atmosphere, and most of the blue has been filtered away from us, leaving us with the longer, redder wavelengths.
When the sky is filled with smoke, there are far more particles in the air to scatter light and the colors are more vivid.
Similarly the sun appears dimmer (more light is scattered) and redder (blue light is scattered more than red. Much of what reaches us is the red.