The IIAR (International Institute of Ammonia Refrigeration), in conjunction with ANSI, issues guidelines for identification of ammonia lines. There is a publication:
Bulletin 114 - Guidelines for: Identification of Ammonia Refrigeration Piping and System Components
(Date: 1991)
Member Price: $10.00
Non-member Price: $20.00
"This bulletin provides a comprehensive ammonia labeling scheme for companies in need of an identification system that "covers it all." It offers recommendations on label sizes, colors, installation locations and label material requirements."
From Tape Selection Guide for various ammonia refrigeration system components, accessed by a link at
ammonia piping must be labelled as to physical state (liquid, vapor, or both) and pressure (high or low).
Regarding IIAR Guidelines colors, see the photo for Ammonia Marking Tape at
How it appears to my eyes:
The name 'AMMONIA' is in black text on yellow,
'LIQ' is in black on orange,
'VAP' is in black on blue,
'LOW' is in black on green,
['HIGH' isn't shown],
and flow arrow '-->' is in black on yellow.