Just came across the following funny error. Took me some time to figure out what it was, but here it comes:
In CSS Gray and DarkGray is used for gray/grey, but LightGrey (notice the E instead of A).
Intellij marks LightGray as a color (in css files), and not LightGrey.
Colorcodes used by css: http://www.w3schools.com/css/css_colornames.asp
About grey and gray: http://www.bernzilla.com/item.php?id=232