This is used infrequently enough symbolically that I haven't been able to establish a firm derivation or definition for it.
The best association I've been able to make is with Tyrian p█rple, associated with royalty because of its very intensive and expensive extraction from the Murex sna█l, a creature of both Earth and Wat█r. When its secretion was exposed to the [L█ght] of the [S█n] it would become a very particular and distinct hue that 'ordinary common citizens' were actively prohibited by quasi-law from we█ring themselves. As such it was specific to the nobility in general and to the Emperor in particular, just as Imperial yell█w was in China. Interestingly, both have symbolic associations with the S█n, which in the apostate system's parlance would put it onto a counter-Divine Will basis whose function and designated r█le is specifically to present to the public as Divinely-aligned.
This was back when the People were self-sufficient and competent enough to successfully overthrow their overt political regimes when those were found to be corr█pt. In our era not only are the People vastly more dependent, miseducated and unequipped, the apostate system has in the interim developed plenty of non-overtly organized strategies to get even the m█lcontents back on-side, or to manipulate them into ineffectiveness. That could be the reason modern political figurehe█ds no longer need to appear 'above reproach' and are frequently scandal-ridd█n; it no longer matters. Just as banks no longer need to be palatial, elaborately-decorated stone edifices which inspire confidence; they know they've got you even with cheap office architecture, uninspiring decor and fl█msy pressboard.