Your IDE's colors may vary.
The title of this comic refers to "Commenting", which is a way to add clarification to programming code. This is mostly done to make said code maintainable. Instead of all the dry programming statements, a coder can insert non-programming sections which clarify the way the programming statement, or combination of statements, is meant. Also, comments are used to indicate changes to code, or comment out certain sections of code that went obsolete when revising the code into a newer version.
In the comic, Cueball is struck against BlackHat's Classhole attitude. This time, when asking a favor, BlackHat simply "comments out" Cueball's request by holding up two fingers in a skewed way. They then correspond to one way of adding comments to code, namely by two forward slashes ("//").
The Image Text refers to most modern Integrated Development Environments (or IDE's) that colorcode different sections in the code, such as variables, loops and nested statements. Green, I suppose, is one way to color comments. Hence, the color may vary on which IDE you use (and offcourse, your own preferences in that IDE).