OK, I have just thought up the strangest idea.
Make some jello. See if there is a way to borrow/make a loop to try to streak the jellow with.
If you could find something similar to the dishes you use, then this would be awesome! :chuckle
Now, what to grow, and how to make it not melt..... don't ask....I haven't thought that far ahead! LOL
If you're just needing practice making streak plates, this just may work!
As for the stains....make a list of directions, repeat over and over and over!