I think the biggest problem people have when drawing with crayons is that they regress to being five years old again. They hold the crayon like they're coloring again, instead of applying it like a fine art medium. Another problem is that many people want to make it perform like colored pencils. While similar in application, they are quite different. You should not use crayons and expect them to behave like colored pencils. You'll be setting yourself up for disappointment.
There are lots of ways to tint your fabric for embroidery, with the most common being crayon tinting. In this post, you'll learn a few methods to try. With all of these versions of tinting, it's best to add the color before you start stitching. While it's possible to add the tinting after your embroidery is finished, it's much harder to color all the way up to the lines and without getting markings on your thread.