I am not familiar with R. cumberlandense seedlings but I don't know of any problem this could be. Many new leaves come out red so I am guessing this is one of those cases. Cumberlandense is a late blooming orange to red-flowered azalea. It is normal for red azaleas to have red new stems. I would be surprised to see red stems on a white azalea. That I would call a problem of misidentification.

Here is a link that might be useful: R. cumberlandense

I grew some azalea seedlings a few years back and many of them were red ... I somehow got the impression that it was a reaction to the warm colored fluorescent bulbs, as if the reddish light simulated fall and caused the leaves to turn.

Thanks for your thoughts, rhodyman and mikeybob. I was concerned because a substantial proportion of the reddish seedlings seem not to be flourishing.

It is interesting also that not all the seedlings have reddish leaves (the stems seem more uniformly red). A very few that, as an experiment, I grew on top of thick, live moss, but otherwise treated pretty much the same as the ones in flats on sphagnum moss, are a fairly bright green and are growing relatively strongly. I have them all under 40 watt white fluorescent lights, which I recently replaced in case they were not getting enough light. So, I just guess I'll wait and see what happens. Maybe this is within the normal range. (I have a few R. calendulaceum, flame azalea possibly related to cumberlandense, also showing some redness, but not so much, and the few I have seem to be doing all right.)

Thanks again.