When you use long exposure times, you will get some digital noise due to the way the camera works. I am certain that what you see isn't stars.
Imagine a grid of photosensitive spots. Each spot gets light as long as you have the shutter open. Some spots register red, some green, som blue. When reading the light value of the spots, the values of the neighbours are considered in order to get the correct value for all colors at that spot. If for some reason the neighbours have low values, a blue, red og green pixel will appear on your picture. How many depends on the camera and sensor, and the algorithm for calculating the colour values.
To reduce this, you can increase iso slightly, and decrease exposure time. You could also look at getting a lens with a lower f value, which means that wider apertures and more light can come through. The result of doing that is blurring in the edges (which won't matter with moon shots)