I don't guarantee that this will exclude a dyed anemone. I do feel that this will help you select a healthy anemone, which I think we can agree is usually not the case when an anemone is dyed.
Actually, in the short term I'm not sure I agree. Anemones do tend to linger for a very long time while declining, after all.... it's what gave them the reputation of 'hardy' in the early days of the hobby. In the short term, in the couple of weeks immediately after being dyed, I think it likely for the anemone to still exhibit 'healthy' traits. After all, the only thing the dying causes problems with is the anemone's utilization of zooaxanthelle. And one thing the marine aquarium hobby has shown is that anemones take a long time to succumb to starvation.
Still, even if the anemone is dyed, if it's healthy to begin with it has a lot better chance of surviving long enough for the dye to fade.