Brew that has strange discoloration/texture.
Sometimes this is nothing more than normal fermentation. This can occur from vigorous fermentation which can cause pressure to build up in the fermenter. A way to prevent this from happening is to swap out the airlock for a piece of hose. Fit a piece of hose of approximately 1 inch into the top/open bucket/fermenter and run it to a container of water. This would also be the method to consult if you don’t have an airlock.
Another more obvious reason for this is mold. Luckily mold can be scraped off the top without affecting the beer’s flavor. However, it is recommended that you take a sample first and taste it. If it tastes grotty and disgusting, then it’s best to discard it. If not, then there shouldn’t be a reason to throw the beer away. Mold beer infections are not harmful. The key is to keep everything clean, spick and span! Cheers!!