blue, red and green. The blue wavy lines are known as Edit and Continue issues, meaning that you can make change to your code without having to stop the programme altogether. Red wavy lines are Syntax errors, such as a missing semicolon at the end of a line, or a missing curly bracket in an IF Statement. Green wavy lines are Compiler Warnings. You get these when C# spots something that could potentially cause a problem, such as declaring a variable that's never used.