Does black interior of a cocotte/dutch oven such as Staub create problems with accidentally burning ingredients/fond?

I avoid dark-colored pans when I want to watch the color of a transparent or translucent mixture, such as cooking down fond or making caramel. (Situations where I need to make a split-second decision on when to stop cooking.) But I agree with GdD -- other things, like onions, are easy to watch in any color of pan.

The color of the interior of a pan isn't going to effect how food cooks, but you are right that a dark pan does contrast differently from a light or metal pan. My own experience with pans of many types is that color doesn't make any difference in the end result, I can tell if onions are browning on a dark cast iron pan just as well as a light ceramic coated pan or steel pan.

If you are concerned about it just look at the food on the spoon as you sauté, the spoon is the same color no matter the pan you use.

I love my Staub dutch oven. I don't feel that the black color of the enamel is a problem. You express this concern:

I am worried that it would be very difficult to discern if it's starting to get burnt and turn black against the black interior of the cocotte.

When I'm cooking, I'm not specifically making fond. The fond is a (desirable) side-effect of the cooking process. The color of the pot doesn't hinder me in any way to be able to correctly cook whatever ingredient(s) I'm cooking. I'm not judging the cooking process by the color or appearance of the fond in the first place, so while it's true that the black color can make the colors of the fond a bit less visible, that doesn't affect the cooking process.

That addresses the question you asked. But that said, I will also share that the enamel surface of the Staub is somewhat more of a matte finish than what one finds in a Le Creuset, which does make cleanup a little harder. When the fond is deglazed fully, it's fine. But on occasion, something goes wrong in the kitchen, the food gets overcooked, and then the stuff that gets stuck to the pot can be harder to clean up than if the surface were more of a shiny glaze.

There are pros and cons to both brands of enameled cast iron cookware (and others), but I don't feel that the quality of the fond is among those concerns. Either type of surface works equally well for that.

YES, the dark interior is an issue for me, for now.
I practically live for beautiful mailliard & fond, but am not an extremely accomplished cook. I went with Le Creuset pieces strictly because of the light interior.

SIDEBAR: I need to work on heat control when searing in enameled cast iron so I don't burn fond. Instant Pot released an electric dutch oven with !adjustable braising temps! and its cast iron dutch oven has a dark interior. (I would love to braise during the summer without having to turn the oven on for hours.)