Both PipeLabels.com and OSHAPipeMark.com offer pipe color code charts that detail the necessary color scheme for labelling pipes based on the pipe’s contents. For example, a pipe that contains toxic or corrosive fluids must be marked with black text on an orange background.
Other standard colors include white lettering on blue to indicate pure gas or gaseous admixtures; black on yellow to indicate toxic, radioactive and chemically active ingredients; and white on green for water and pure liquids.
In addition to the color chart for pipe marking, OSHAPipeMark.com also lists the minimum letter size and marker length for pipes based on type. For example, a pipe that is bigger than 10 inches in diameter must have 3.5-inch letters indicating its contents.