Electricians do it all the time. They will wrap white tape on black RW-90 cables to signify it's the neutral.
True dat and permitted by code. However, it is done at the point of termination inside an enclosure where it cannot make a mess or be seen or accessed.
But this proves the case of an Elmer's ignorance and complete lack of regard of safe operating principles.
I use red tape every 1', to mark black coax cables used to carry B+ between cabinets.
Uncle COW never considered the voltage rating of the coax insulation. Never gave it a thought he is many magnitudes higher voltage than the insulation is rated for. DOH!
There is no code or safety issues using tape to identify conductors, just some ways are better than others depending upon the application. If you like sticky adhesive collecting dirt and debris and sticking to your fingers, knock yourself out, that is what they make Goo-Gone for.
FWIW they do make conventional cable insulation in white and gray.
Sticky side of the tape faces the cable. There is nothing sticky..to get stuck on. I got loads of 1-0, all in one roll, so that's what I went with.
Insulation rating of RG-213 is through the roof. Try hi-pot testing 213-U..... with the braid peeled back 2-4". It's off the chart. Heck, even RG-59 will not show any leakage on a hi-pot tester at 30 kv...... same deal, braid peeled way back.
I have a 200' roll of RG-393 teflon coax. Peel the braid way back...2-4". Good luck trying to find a hi-pot tester that will go high enough. 100 kv will not do it.
At each end of the coax cable used for HV, braid peeled way back, cut off, leaving only 1/2" of braid exposed. cu strap wrapped around the braid, and pinched tight with a single set screw..and also silver soldered. Other end of cu strap bonded to chassis. Loads of strain relief at both ends. Braid is at chassis potential. This is one method to hardwire B+ between cabinets.
2nd method uses special connector's..that look just like bored out SO-239/PL-259, and modified, so they have a long white plastic 2-3-4" long piece inside em on both halves of the connector. Banana plug on end of center conductor mates with receptacle at other end. They are rated for 10-20-30 kv.... and designed to fit RG-213 U.... and are stupid expensive...and yes, they are UL rated.
Now if you really want something to sink your teeth into, forget the non-UL rated ASTRON supplies. Take a look at the
CHINESE variacs, the RED ones. They are DEATH traps. Fixable, but what a bitch. Everything stupid u can think of, like fuse in the neutral leg..along with the flaky switch. Non existent case grnd. And 120 vac sitting just .002" away from the case...which of course is sitting insulated via 4 x rubber feet on your work bench. It's all over the internet.