I've searched for this but can't seem to find an answer. If it's out there and I missed it, well, I'm sorry 
I was using #define PRESSED 0, for use in if(digitalRead.(pin#)==PRESSED){ }. It works. My question is why does the word "PRESSED" show in blue text? Is it truly an Arduino literal or is it part of the C pre-processor. It's not critical, but I don't want to put it in a lot of code and then have to rewrite all of it after some change to the Arduino IDE.
In library folders you will often find a file named keywords.txt which contains a list of key words pertaining to the library. The contents of these files cause words in the IDE to be coloured to make them stand out as keywords. However, the mechanism is useless because the colour coding is picked up whether or not you have included the library in your program.
In your case the word PRESSED must be in a library keywords.txt file on your system.
In library folders you will often find a file named keywords.txt which contains a list of key words pertaining to the library. The contents of these files cause words in the IDE to be coloured to make them stand out as keywords. However, the mechanism is useless because the colour coding is picked up whether or not you have included the library in your program.
In your case the word PRESSED must be in a library keywords.txt file on your system.
That's good to know. I've wondered about that myself once or twice but never looked into it.
Thanks for the info.