Here's my take. Not damping off...that kills them at the soil line...the stem shrivels and they just keel over.
Sun scald can grey the leaves, even through a window. And you can't leave them inside for a week and then place them outside in full sun. This will also scald them. They need to be hardened off gradually(start in partial shade and protect them from wind...it also can do damage). After their week indoors you should have started over with the hardening off.
Keep them inside a little longer under lights until they bounce back, shed their damaged leaves and start to grow new ones...then start the hardening process. HTH

Clearly it is sun burn (sun scald). You gave them too much direct sun too quick. Start them out in shade the first couple times and then partial sun and eventually full sun. Also, slowly increase their time outside each day. Putting a plant out that isn't used to direct sun in the full sun for an hour will sun burn it. Those leaves that are "greying" will likely die depending on how bad it is. you will notice that in most cases they are the bigger, older leaves lower down on the plant. Those are the leaves most susceptible to sun burn. Don't sweat it if just those die. If you have worse sun burn and all or most leaves are burnt, then you may have an issue. Treat it like you would a person and bring them in for a while. Then start over and work up to full sun for prolonged periods.

FYI: Sun through a window is not the same as direct sun. Most home windows have UVA/UVB filter protection built in to them so the plant is not exposed to "full" sun through the window.

Bruce

Thanks for the feedback. You won't be surprised to know that I was working outside the whole time my plants were in the sun, and I too got a nice sunburn on my back.

Live and learn....

Yeah, mechanically speaking plants are like humans, they're lazy. Producing nice thick cell walls that protect them from too much sun and wind requires extra effort on the plant's part, and much like a human if it doesn't have to do extra work, it won't. So, the direct sun beats straight through the thin cell walls and literally burns out the chlorophyll in the leaves, and the wind snaps the weak stems like twigs.

Like was said, you have to gradually increase their exposure. Just enough light for them plant to realize it needs extra protection, but not enough to actually damage it.

Sort of like humans in the spring. Our lily white hides from being indoors all winter need to slowly build up a tan before we can just lay around in the noon summer sun all day without burning to a crisp.

Edymnion: Can't we just spray some SP50 on them and kick them outside?

...I know you're joking, but seriously... has anyone actually tried that? I mean, if window glass comes with UV blockers and thats why plants won't normally burn in a window...seriously, has anyone tried putting sunblock on a plant?

LOL, I haven't. But if I have a spare plant when mine get big enough, I may break out a bottle of the spray sun block and douse it down and throw it out there in the direct sun. It would be a fun experiment. Problem is, my plants are way behind schedule right now and are only a couple inches tall.
If you try it Edymnion, keep us posted on how it works out. One should probably put an untreated plant out with it to see what difference it makes or if the spray damages the plant somehow.
Bruce

Yeah I know. I just had to restart my main batch as well. The overwintered stuff is in the ground, and the first batch of bhuts is doing okay, but the douglahs and butch T's I planted last month in the self watering starter never sprouted. No clue why, the soil stayed moist but not wet, they stayed at least at 70 degrees at all times (and higher when it was warm out), but nothing.

Stuck some additional seeds in the tray with the old ones, put them back out in the warmth, figure either the new ones will grow or they'll both pop up for double the superhots.

I don't know about SP50 but I can tell you not to use Deep Woods Off on your plants!

Here's a shot of a previously vigorous potted Black Cuban ornamental that accidentally caught some stray spray. Two days later it looked somewhat cooked in some area. After I saw the plants reaction, I stopped using it myself!

Edymnion: 70 is too cold for Chinense seeds. It can take several weeks at that temp to germinate. Get a heat mat with controller and you can sprout them much faster.

70's as a low is not too cold. They got 70's at night indoors, 80's outdoors during the day. Few days it rained, they stayed indoors for that.