Hmmm… I get this on some of my outdoor herbs each season, but in that case it’s just a normal progression of life, and my herbs do not fare any worse for the wear. Occasionally a leaf or two will begin to die, but I just pinch it off and all is well.
Indoors, I’ve had some houseplants get a bit odd spotty like that. To me, it gives me the impression they feel a bit faint, if that makes sense. I don’t know the cause, sorry. Do you rotate your plants so they get more even light exposure? That’s one of the first things I do when I notice a houseplants looking a bit under the weather. Sometimes a plant just wants a change of scenery! Then I check soil, water if needed, and maybe give a bit of plant food. That usually does the trick. And I check for dying leaves or blossoms and dead head regularly too.