Not as a matter of law of course, but as a matter of custom. Every candidate, Democrat or Republican, always uses red, white and blue as the colors of their campaign materials. When was the last time a candidate in a major party used other colors? Would such a candidate have any chance of success in today’s campaigns? Or are they just not willing to take a chance, and be labelled ‘Unamerican’.
The only possible answer is yes.
They have to be red, white, and blue. No other choice allowed. All the way down to the local level.
Except for the Green party. But they’re commie furriners.
I seem to recall Mark Russell (remember him) noting that the designer of the podium at a Democratic convention had described the color scheme as salmon, eggshell, and azure. Actually, I seem to remember some editorial comment about this as well, so it may well have happened.
There was a sheriff election in 2008 in my county. It was huge deal, and there were yard signs, bumper stickers and billboards all over the place. I think I probably saw five sheriff signs for every president sign. I saw about an equal amount of signs for the two candidates. One was all red, white and blue, and the other was green and white.
To this day I have no idea who these two guys were, what their stances were, or why this election was such a big deal. And just now after reading this thread, I decided to look up who won. It was the green and white one. Which is good, because I think I voted for him.
I was a heraldry buff as a kid, and I consider reuse of the same color scheme to be a way of not differentiating yourself from the norm.
When someone is different enough to come out with his own distinct color scheme as a candidate, that’s someone who wants you to take a hard look at him, & who may think he can survive that look. Not a typical pol.
I thought of the Green Party when I read the subject/title line.
Just to provide a foreign datapoint, political signs in Canada are always the colour of the candidate’s party – Liberals are red, Conservatives are blue*, the NDP is orange, and the Greens are green – and usually have white for contrast.
This scheme has not given the Liberal party – who use the red/white one would associate with Canadian patriotism – any advantage.
*These first two are especially confusing to this American, who’s used to the colors going the other way.
Just as a little anecdotal aside: there is a local city councilor here who runs a funeral home. His campaign signs are black and orange. It works out bc campaign season and Halloween season overlap.
Getting back to the OP…slight hijack, sorry… I too have wondered not only about that, but about the colors of the presidential candidates ties. Sometimes it seems to me that for big appearances and debates the democratic candidate will be wearing a red tie and the republican candidate a blue tie. Any truth to this or is it just confirmation bias?
I also seem to remember hearing that once, fairly recently, the two presidential candidates had been scheduled for a major appearance wearing the same color tie. So at the last minute their staffers got a hold of each other and coordinated a tie change so that their candidates wouldn’t show up wearing the same color tie. And now, allegedly, the staffers of the campaigns always check with each other to make sure their candidates don’t show up to the same event wearing the same thing. Does anyone happen to remember when / if that happened, or whether anything like that happens?
Man, a tangentially related anecdote and attempted hijack. I am an awful person, sorry. 
Actually as I recall there was a story I heard in the 2008 election that green was the color of choice for campaign signs. Apparently the idea was to associate the candidate with the color of money. Unfortunately I don’t have a cite.
Ron Johnson (Rep. Senator from Wisconsin) had green and white signs and stickers in Nov. '10 when he ran against Feingold. I think Paul Wellstone (D - MN) had green and white, also.
Carl Paladino’s most recent run for NY governor used orange and black. Yes, it came across as ridiculous as you’d expect.
http://www.campaignbuttons-etc.com/NY19Bpaladino.jpg
http://www.citizens4freedom.com/Portals/TeaParty/Carl%20Paladino-1.jpg
Not roan?
Well, black red and green would probably be a bad idea for Obama.