One thing I have learned about watercolour is that it can have a mind of its own when it hits wet paper, and it takes some practice to control where it goes or the depth of colour as it dries lighter than when you first drop the colour on the page.
There are a few basic rules to follow if you want to try a starry night, and that is to build on the colours, and start with the lightest color first and then work your way to the darkest. Check out the video below to get you inspired to take a stab at watercolor painting and try this beautiful starry sky. There are no intense details to worry about and it is all about the right colours and effects. Check it out.
A couple of things worth noting:
To take color back off of a watercolor painting - As long as it is still damp you can remove color or the depth of the color by using a clean damp brush and gently but firmly go over the area you wish to lighten or remove and the damp brush will absorb it.
Starry NIght - Keep an old clean tooth brush around for the stars. Using acrylic white paint dip the damp brush into the paint and then spray for the stars. Practice on a bit of paper first to get the right technique. This artist above does a beautiful job of the night starry sky. The colors are beautiful.
Next time you are out walking at sunset, take note of the sky. See where the dark and the light are, and take a mental picture or use your phone if it will pick it up to make your next starry night watercolor painting realistic. You could do tops of houses too for a different look instead of the trees and mountains.
The trick is to PRACTICE PRACTICE PRACTICE and have fun with it.