You can find tons of helpful info about mutation & coloring at websites below, our aviary refers to those websites very often and wanted to share this information with you.
Budgie world has enormous colors and varieties. Please refer to WBO Color Standards, where you can find most detailed descriptions of all varieties and colors as far as the World Budgerigar Organization requires and is also used by the US national societies. Unfortunately, there are no pictures. Set up well and by clicking on the specific bird in the index, you are taken directly to the description and standard requirements for that color or variety.
Also, please refer to this great website for budgie mutation and color guide with pictures: