Looks good to me, does like regular misting, but looks like you have it under control, no cracked leaves to show over-watering, and the old leaves do get absorbed, that is what is happening there. Keep your focus on the smaller new leaves, they grow well, you are good. Here is a plant that had 4 leaves when I got it in 2007...

Sorry, this post is redundant. I thought my other post didn't go through. Oops! :) (Would still love any advice though)

I sincerely apologize for the delayed response! I never got any notification of replies to my question so I assumed there were none. I came back on here today because I have a new problem with my marshmallow. I have got them hardened off and they are all outside near my patio. They are definitely growing better but in the last few days, have all gotten purple leaves (still only a very minor issues with the yellowing)! It is only effecting the oldest of the leaves so far but the stems have turned purple too so I'm worried that whatever this is will make it to the beautiful newer leaves as well. I haven't put them in the ground yet because I am terrified of pests destroying them. Something, I think we've come to the conclusion it's birds, has taken every one of the 30 clary sage seedlings and 2 of my comfrey seedlings that I transplanted out. But why on earth would the marshmallow leaves now be turning PURPLE?! Gardening is supposed to relaxing

What kind of pest? Why do you think that?