I'm an accountant, and I've NEVER heard of this so called "black suit standard" in my life (because obviously, it doesn't exist). Every job fair I went to during college suggested grey or navy suits for interviews at a Big 4 firm.
Also, accountants work in every industry on earth, so you can't even put a "standard" for them. At my current firm I wear nice clothes to my "high end" clients, and I wear jeans and casual boots/"dressier" sneakers to clients that are startups. We team up with accountants from KPMG, Deloitte, etc. during audits and those dudes don't wear suits at all.
If someone told you that he wouldn't hire someone not dressed in a black suit, then that employer insane and a complete idiot that you shouldn't be working for anyway