Oh, that is a nice image! But good to know, that this is trendy, as my cousin is working on a website with such coloring submittals herself atm.
If someone is interested, I will post the link when she is ready and the site is online.
I myself was evil and took some images from the Simon's Cat books for coloring
They have a lot of very detailed nice sketches:
It will take ages before I will be ready