Enameled Dutch ovens, pots etc, will over time firm a yellow brown coating. Do not remove that coloring. It is actually seasoning the enamel. We have quite a few Le Creuset enamel cast iron pans and Dutch ovens. Ours can go higher than 375, as long as they have the metal handles. The ones with plastic lid handles are limited to 375. My favorite one that I use all the time is this sauce pot! Currently full of Au Jus!
The lid handle is plastic and can only go to 375 in the oven.