I admit this is something I've tried a bunch of times and I don't feel like I'm very good at it. But, in the spirit of the challenge I decided to give this another chance.
Once the line drawing was complete. I scanned it in and loaded into GIMP to crop, add color, and scale the drawings.
This is a picture of the computer screen showing the first round of coloring I tried.
Here is an idea of how the button looked. Something was off with it, right? The letters were too muddy and the top of the mushroom popped in the wrong way. But, this is why I like using a digital editor so much. It's a few clicks to change the color around.