Sounds like the iron wasn't hot enough and left on long enough. Try doing it on a test and hold it there until you see melt off on the paper towels. If you think it needs more color then, add the more color and set the iron back on it with a diff paper towel so you know when it has lifted it to the paper towel. Then as a added bonus when I get all done, I soak mine over night in vinegar. And wash. When I take it out of the washer, if i think it needs more color I go ahead and repeat the steps above. I love using crayons.
Tammy