Coloring a picture can be done with Poodll Assignment Submission. There may be other plugins to, but I have no experience with them. You set it up as an Assignment with submission type of, Online Poodll, with Poodll Rec. Type of, Whiteboard, and a Poodll Whiteboard Background of the picture you want the student to color in. You also need to set the Poodll Whiteboard size to fit the background picture size.
When each student clicks, Edit submission, they see the whiteboard drawing editor with your picture already there for them to color in. The picture remains even if they need to erase part of their coloring.
I know this works with png backgrounds, but will probably work with others, too. This works pretty good with just a mouse, but, much better with some kind of tablet and pen.
The only downside to all this is that Poodll Assignment Submission also REQUIRES Poodll filter and Poodll filter DOES cost money. When I was actively still teaching, I just paid for an annual subscription out of my own pocket. However, you can do a 30 day free trial to see if it does do what you want, before committing to any payment. Just don't be shortsighted enough to think the money is not worth it for your students to color one or two pictures. The whole set of Poodll plugins that you get to use with the filter is simply staggering when you figure out and see what all you can do with it, especially when it comes to audio and video capabilities for teaching a foreign language, such as English. Along with the whole set of plugins, there are literally DOZENS of widgets available for use to enhance your site, lessons, quizzes, assignments, etc. A simple for instance, you can add a user or username filter that will personalize your site so each student is greeted by name when they log in.
The Poodll developer, Justin Hunt, is active here in the forums, and is always quick to help, if you have any questions. What always impressed me the most, is that he is also quick to respond to feature requests, if at all possible. I can remember once making an idle remark, "It would be nice if......," (can't remember exactly what I wished for) but four hours later there was a new version out with the new capability.