I remember one time, when a guy got all excited because the "Flammables" cabinet had been painted blue. They have to be yellow, he claimed. Open up a catalog from the manufacturer, and -voila!- there were 'flammables' cabinets offered for sale in just about any color you wanted. Guy claimed it was in the NEC. Nope. Then he claimed city code. Nope. Claimed the fire code. Nope. I finally told him to find it himself- and until he did, the cabinet was staying blue.
Or, we get into this regularly on the 'grounds up or down' debate. Let me sum all this up very briefly:
Just because it's "always" a certain way does not mean it HAS to be that way. Check your assumptions. Nor is it proper, IMO, for the code to mandate things for the sole purpose of making life easier for the inspector.
The colored Romex is nothing but a marketing ploy, one that was so successful that everyone copied it. I know one contractor who special-orders his romex in pink, for the specific reason of deterring theft from the job site.