I was writhing a sketch and went to name an int "speed" however the word turned orange, as far as I could tell as I am partially color blind, as if it was a function or something. When I searched the extended reference section of the website I found no mention of such a command.
'speed' is defined as a keyword in the stepper library, but there should be no problem using for a variable name in a sketch. A quick look at the stepper library indicates that speed is actually declared as private so it probably shouldn't even be in the keyword file.