Prepopulate multiple checkbox fields from one form into another

I need to pull multiple checkbox data from a form into another form. I have read the pre-population guide on the Formstack information/help site, but I cannot get the code to work. Can someone help with that?

Example:

Form A multiple choice question: What is your favorite color?

Answer options:

Red

Blue

Yellow

Green

Form B needs to pull in which color was chosen.

What is the code to do that?