During the late 1990's teams started developing corporate colours in an effort to establish their brand. This was the dawn of the closed grid and the value of teams was skyrocketing (even Arrows were valued at over $150m

).
McLaren opted for grey (and black) just like Ferrari is red (and white) and Prost was blue. Jordan tried to corner yellow. Some teams successfully managed to get their sponsors to tow the corporate line although in most cases a major corporation simply bought the livery and then resold it in some way or other. Mercedes paid for the silver livery and then got others to adjust their sponsor colours accordingly (like mobil 1 and West) by offering a discount. BMW did the same at Williams and got compaq and Fedex to change their colours.
Yet for the smaller teams, this was always been a bit of a pipe dream. Jordan might have been yellow but if the right sponsor came along, he'd change his colours pretty damn quick...
And to some extent, that goes for the other teams as well. Ferrari may well be able to insist on red although that has been watered down over the years. I remember Enzo saying he didn't smoke (Marlboro) or drink (Martini) but over the years, Marlboro has appeared on his cars and red ain't so traditionally red anymore...For the right price, we might see blue and yellow Ferrari's....
And that goes for McLaren too. If faced with the choice of money and surviving or maintaining a brand image and going bankrupt (or not getting enough money to remain competitive and eventually becoming a Tyrrell), every team IMO will opt for the money.