jpeg – Why is the night sky photo showing uneven color and strange pattern in background?

Colors of the stars

Very small light sources are a problem with the rendering of color from the sensor. Basically the star itself is not much bigger than one pixel, but you will light to some red, green and blue pixels. This can lead to the color of the stars going off, depending how many of the rgb pixels of the sensor get some light from it.

On larger light sources, the color would even out, but here a shift can occur.

Then, with small light sources, chromatic aberations might become more distinct around the lights, affecting the color as well.

A last effect is high iso noise, why can also contribute.

Color Patch

This sees to be light pollution from dust in the atmosphere which lights up with the lights of cities nearby.