Depends. I ran a business that was 100% in white, we declared every penny of income, paid every single penny of taxes due and we were still profitable. Not very but we were. Doing it otherwise wasn't an option for many reasons, not the least of which we were audited annually by EY.
If you're asking biz owners on a public forum to admit to a) fudging on their income taxes and B) what percentage, you're prob not going to get a lot of responses
Yes, many businesses do operate mainly in black. Typically they declare enough to be realistic, give them a reasonable income and the rest goes off of the books. But if one chooses to go that route, you had better be very smart and circumspect about it. Alternately, find yourself a very good accountant who will do everything possible to mitigate your burdens while still keeping you in white (or at least a pale shade of grey).