In Graphic Industry we have often substrates that are non 100% opaque - which means we have to standardize the backing surface. There are two basic ISO standards that create guidelines for proper backing.

White Backing — ISO 13655: 2017

White backing is the most important backing for color measurement. Most common ICC profiles and characterization data sets are created on white backing!  ISO standard has been updated due to white backing specification and today a key part is the "spectral tunnel" where the spectral range for the visible part of the spectrum is defined individually for each 10 nm. Additionally, some other parameters are specified. No OBAs are allowed.

Black Backing — ISO 5-4

This kind of backing is critical for double-side printing - to reduce the impact of back printing black backing is used. The results of measurement are changed due to the white point shift - which causes SCCA correction a mandatory for color evaluation!

Substrate Inspector

White and Black Backing measurements are used for Opacity evaluation. For this purpose, a dedicated B&W Backer has been developed.

The top white and bottom black parts are used in a sequence of measurements.

CC 11x17" XL Measurement Backer 

ChromaChecker offers backers that are ISO compliant. Size: 279x 449 mm. 
The current version 2 has a label on the back - black side (on picture ver.1)

 Internal ChromaChecker QC tool report for White ISO compliant evaluation.