I think they are being scorched by too much light. Remember most seedlings certainly start somewhere hot but with low light levels. I suggest weaning them off the severe conditons to natural light in a sunny window with good air circulation.
Myles

Here is a link that might be useful: Leaf pigments.

Hello Jonathan,
Your Passiflora Picturata has reddish undersides to its leaves because it is supposed to. My seedlings are the same. I imagine that you got your seeds from Mauro Peixoto in Brazil - you could ask him to confirm. Otherwise check out Myles Irvine's site in the UK as he has a poster("etching") which shows that the colouration is entirely natural to the plant. Hope this helps - Best Wishes,

Foliage that reddens is not "scorched" by too much light. Scorching is when actual damage is done to the leaf tissue.

When plants turn reddish/purplish because of the light, a chemical compound in them, called an anthocyanin, has been activated. This leads to reddening/purpling. Some people say that since it might be acting as a defense mechanism to the light(like a suntan on you or I), that it's a bad thing and to be avoided. Still others feel as if it is as harmless as a suntan.

I belong to the second group and if a plant has decided to color up, I let it. Plants need all the light they can get short of scorching and this is one way to make sure you're giving them all of the light they can handle.

Sam

Sorry folks.
Best to check out Jonathan's pic at http://www.passionflora-images.com/ before commenting, and his text elsewhere, which is, ''Can anyone tell me why the leaves on my P. Picturata seedling a turning reddish maroon? It is about two months old and 8" tall. It is not the new leaves starting red, then turning to green like some passiflora. It is in a small closet on the shelf with high intensity lights and a fan. It stays about 85 degree F (30C) during the day. It is in the one of my three seed trays which does not have bottom heat. Humidity is high and I give it a little water daily.''

The image site is a nuisance because right click is disabled but the pic is the top post on the front page. The colour change is on the top of the leaves in patches and is not the normal anthocyanin pigment production. It is scorth damage in my opinion. Temps that high are good for germination but high intensity light is not good for young seedlings once up.
Myles

Here is a link that might be useful: Passiflora pigments.

Looks like standard anthocyanin darkening to me, but I am not a botanist. Feel free to come to another conclusion.

Sam