I started some marigolds a few weeks ago. I noticed when a couple of my seedlings got their first true leaves that they had very "even" black spots on the new leaves. By even I mean on every pointed part of the leaf, along both sides of the main vein, there are spots. They are not irregular at all. I wasn't sure what it was but it didn't really look like typical disease behavior, so I left it. Now that all the rest of my marigolds have true leaves, I looked closely at all of them - and all of them have it! Except that on many of the spots are the same color as the leaf; you can tell they are there by the slight raised area. I can see that all of the newly forming leaves have them too.

I've never grown marigolds before, so I don't know if this is normal. Other than the spots, the plants look completely healthy. What is it?!