I don't have a tabby cat, but I have 2 calicos, and the shorthaired one (Bird) has several of these in just the spot you described, and they are just part of her coloring (and she will be glad when I finally remember this and quit absentmindedly trying to clean it off!-there's not much hope for that- she's 13! ) . If they aren't raised, and they aren't changing, I would just ask your vet next time she goes in. If you're really concerned, call and ask .
My cat is black, and has areas like that between her eyes and ears. When I first got her, I thought it was something gross, like ear mites. But the vet said that's just her natural coloring, and since the hair is thinner there, you can see it more easily.
Do they look like new "beauty marks?" My boy Fatty has them...in the corners of his eyes, and new ones always comming in around his lips and nose. I was worried, and took him into the vet. My vet said it's basically to do with age...along the lines of liver spots, I think. But he said it wasn't anything to be worried about, and it's not a skin problem, it's just to do with age! If you look on my catster pics of Fatty, you can see it. Hope that helps a bit!
Gizmo has freckles between her eyes and her ears. She may have them elsewhere but the fur is thin enough in this area so that I can see them.
No one at the vet's office has said anything, so it's probably just an area of darker pigmentation. In other words, a freckle or 'spot'.