depend on the color of the sheet,if it's a plain white one i think you can get away with using red or blue but black is recommended,for a colored one(doubt you will see them very much though) i would stick with plain black as it would get to hard to read if not..
red
the color of mars is orange.
a sign up or a sign in sheet/box
It Appears to be Red but it is actually gray.
Mar
Must patients sign in to an office
blue
Blue
line spreet sheet
Rampancy.net has a lot of free sheet music. You have to sign up, but sign up is free.
whiteIn California, the color of a regulatory sign is:Black and White
red