How to handle color codes when trying to use grep, sed, etc

I'm trying to use sed to process some output of a command that is generating colored lines (it's git diff, but I don't think that's important). I'm trying to match a '+' sign at the beginning of the line but this is being confounded by the color code, which precedes the '+'. Is there a simple way to deal this this issue, or do I need to use some complicated regular expression to match the color code.

If possible I'd like to preserve the coloring of the line.