Yellow What?

This is why I shouldn't check my email on the weekend:

As of 6pm Saturday evening, Library X is quite cold, perhaps due to a hot water problem from yesterday's outages.

Also, there is a new ceiling leak, a yellowish color, on the 4th floor near Vampire Librarian's desk. I have informed Facilities of both problems.

--The Boss

Why is the leak YELLOW? And how close to my desk? Is my chair safe? My plant?