Specific for lamb, this study aimed to test the effect of Nix Pro Color Sensor (NIX) repeat measures on the precision of L*, a*, b*, hue and Chroma (colour traits); compare colour traits captured using the NIX and HunterLab MiniScan (HUNTER) instruments; and establish the impact of NIX settings (Illuminant and standard observer) on retail colour stability. This used the longissimus lumborum muscles from the right-side of 150 Merino carcasses were sampled and then aged in vacuo for 5 days. It was found that six repeat measures were appropriate in general to achieve precise colour data for lamb meat. Observed colour trends over retail display were analogous, but not interchangeable between NIX and HUNTER instruments—except for a* data which was comparable between instruments. Only b* and hue were found to be impacted by NIX Illuminant and standard observer settings, and Illuminant A captured the greatest magnitude change in b* over retail display. These findings support the reproducible and robust assessment of lamb meat colour using the NIX.