The apostrophe '
character is causing Sublime's syntax highlighting engine to think that you're beginning a single-quoted string. Since ending a line with a string "open" is an error, it is being highlighted with the reddish invalid.illegal
scope in your color scheme. It's nothing to worry about, it's just something you'll see happen with SublimeREPL when you have non-closing quotes on a line.
To verify this is the case, try opening a new file in Sublime, setting the syntax to Python, and pasting in the following code:
"This is a valid string"
"This is also valid even though it has a single quote ' char"
"This string is not valid
"""This string is valid, and doesn't have the red line
even though it has a newline, as it's triple-quoted"""
The middle (invalid Python syntax) line will have the red stripe from the end of the word valid
to the right side of the window. The others won't.