not stable yet

[troad]

The following quote from Carolyn in an exchange about yellow tomatoes leads to a new question for me.

"Len, Tom's Yellow Wonder would be a possibility if it weren't for the fact that
I've seen some folks post that it doesn't seem quite stable yet and I've seen
the pictures."

What do I look for as far as unstability and how do I proceed from there? An obvious change would be a different fruit color but what else??