SocketsSticks that are BLUE indicate Metric sizes measured in millimeters. The labels in these packages correspond to those metric sizes, allowing you to organizes your sockets, accordingly.

IMPORTANT: There are two sizes of SocketSticks for the 3/8" socket drive. This is because of the wide range of socket sizes available for a this drive. Please pay close attention to the socket sizes supported by the small base and large base SocketSticks for the 3/8" drive, described in BLUE in the product details.

Also, V-Blocks come in BLUE. This is important if you're organizing Metric size wrenches (i.e. open-end or box). Its not as important for socket drives, screw drivers and other tools that don't have measured sizes. For those tools, you can just pick your favorite color - RED or BLUE.