From LabVIEW Wiki
A System Label is a text decoration found on the Controls>>System palette. It is very useful because it's background and border inherit (adapt automatically) to the block diagram or front panel colors, independently of the colors of possible underlying objects. This makes them useful for labeling wires as a form of code commenting. The corresponding "chameleon" color code is 0x01000037 (d16777271), although it appears as R0:G0:B0 in the LabVIEW color picker.