What IS this stuff? I only have one coleus, and its child, because its the one I like a lot. I've grown these particular ones a lot of times and never seen this cruddy stuff. Help? Please? [Edited to add: No ID]

The crud:


Underside of leaf:


The whole thing (poor baby):

I just view those marks as pigment issues. Removing any affected leaves would likely eliminate the problem. Try it! You have nothing to lose.

What a relief. Surprising that the seedling, now a full fledged plant, doesn't have those issues. I go now to remove offending leaves. Thanks again, pirl.

You're quite welcome. I view them as the happy little "liver spots" we get as we age - nothing fatal.