One of the world's most famous pyramids is not located in Egypt but is on a music album cover by the band Pink Floyd. However, not a pyramid but a prism, the iconic image of a beam of light turning into a rainbow is a powerful symbol that captures the complexities of colour perception across cultures and individuals. This study examines how children can discern colour gradations in mixed reality (MR) environments, utilising the widely employed Farnsworth-Munsell 100 Hue Test. The MR version of the test, adapted for use with the Meta Quest 3, was evaluated with 52 children aged between 5 and 17 years. The results revealed significant differences in colour discrimination among age groups. Younger children had more difficulty distinguishing hues, particularly in the green-blue spectrum. The findings also demonstrate the applicability of MR-based colour assessments for younger children, providing a fast-screening alternative to traditional physical colour vision testing. The study's outcomes are conclusively synthesised, highlighting their implications for colour discrimination in educational settings. [For the full proceedings, see ED665357.]