Dark blue is the way to go. Works with grey, khaki and light brown pants and darn near any shirt. Years ago I worked in a downtown, highbrow firm that required a suit if you would see a client and a sport coat and tie on days no clients would see you. I spent years getting away with Sears khaki work pants, blue sport coat and just about any shirt in my closet. Other guys spent a fortune keeping up with the required dress code while I spent about a third of what they spent. Always carried too and nobody ever caught on.