pizzas don't stick to a pizza stone unless the stone is too hot. Not sure the dark surface even makes a meaningful difference.
The new scorpio pizza oven does come with a dark stone but I wonder if it is just to hide stains
In my outdoor oven the stone can be removed and rotated/flipped over. It looks 100% clean. In a nonremovable stone oven like roccbox or one like Koda 16 where it can't be rotated, I imagine the front takes longer to get clean.
I've never had a pizza stick to a stone except as a result of a tear or as the result of liquid soaking through the dough. I've gone as high as the low 900's F and the bad thing that happened was my malted flour based dough burned.
A black stone will absorb infrared more readily but it's a mistake to imagine that heat is just infrared light. It's not. Heat is a form of energy, and materials emit infared light as a result of being heated. Different materials have different coefficients of infrared emission so the reading from an IR thermometer is always an approximation unless you know the coefficient of the material you are measuring and what coefficient the ir thermometer was programmed with. Bright metal in particular typically has a poor coefficient of emissivity and this is something i have to tell people trying to troubleshoot 3d printers with some regularity. That the reason their $7 IR gun reads brushed aluminum temperature lower than the thermistor embedded in the metal is because of the technology, not the temperature.
A black pizza stone will probably have a higher coefficient of emissivity than natural cordierite, but I'm not sure by how much, or even if that is actually the case. If you really needed to know the exact temperature, you'd need to embed a pt1000 RTD within the stone or something. And even then, you'd want to calibrate it with known temperatures such as the boiling point of water at your elevation, etc.
I doubt that there's a considerable upside to a clean pizza stone. Conversely, the people who recommend "seasoning" a pizza stone should shut up because there's almost certainly no upside to that either.
If you bake on a layer of cheese and sauce, apply more heat until it carbonizes and brush off the crusty bits.
Otherwise, the stains are just evidence of your efforts.