How do I change the colors?
You have to edit the corresponding color-scheme file and change the color code for comments. I.e. if you use the color scheme 'tango' you have to edit
/usr/share/gtksourceview-3.0/styles/tango.xml. Look for the
<!-- Comments --> <style name="def:comment" foreground="skyblue3"/> ..............................
and replace the foreground color (e.g.
Gedit offers multiple syntax colour schemes in its settings. If you don't like any of them you can edit the schema files to you liking and alter existing or create new schemes.