I have a very nice black bitch who has a "bit" lighter eye color than my other girls. How light is too light?

Correct eye color on a black is a "burnt sugar" brown.

Find a couple of lab breeders you trust and ask them to LOOK at the bitch. My description of burnt sugar is probably not the same color to you.

When I look at a dog and the first thing I notice is the color of its eyes, they are too light!

If it's the only thing you notice, then yes, probably too light. However, a too dark eye is, to me, worse than a light eye.

Could it be carrying chocolate??? Sometimes a Bc has a lighter shade of brown???

There are many black known for light eyes. Not always a choc in there, good grief charlie brown !
I don't like light, but also don't like the dark that gives a harsh look in any of the colors.