Sounds like a typical MMC mismatch as found on my Roadster's generic Smith's clock illumination cured when replacing the blown LED with one of better colour match to main instrument illumination.
Your findings with CX suggest the clock illumination is dimmed by instrument rheostat (unlike my Roadster) which means that if clock illumination is via LED it would need to be a dimmable one. If so a similar one of greater intensity better matching main instruments may be an answer, avoiding the need to alter wiring.
