if you want to change to your own colors just edit the CSS code by changing the HEX color code, ie;

/--------------------\
| #AAFF00 ---------|
\--------------------/

Nothing fancy, nothing complex. Just there if you wish to change the default blue color to something else. Hopefully in future Google may implement a color changing option for Inbox.
- - - - - -

UPDATE -- 2014—12—31:

Fixed:- Search Bar would show colors incorrectly, fixed to comment out certain lines.
Added:- A color fix for when selecting multiple emails, so the text isn't blue.