Tom,
That was a great post from Randy Cubberly just above and something we should have considered earlier inasmuch as you're asking re the impact on the judges' perceptions of the aircraft in flight. Give his suggestions some thought and, if the opportunity arrives, discuss it with a judge before a meet and see if they are amenable to (post competition) discussion. For a fair evaluation don't tell him precisely what it is you're evaluating. Then sit back and judge and make notes re the color of the airplanes and "your" thoughts as to how that color affected "you". Then see what the judge has to say when you ask what color the airplanes were and whether the hue had any impact of which they were aware.
FWIW, I just ran through several hundred of the pictures I've taken of stunt ships since the late 1950s--most heavily starting in the early 1960s when I started attending Nats and Team Trials (and a few World Championships). Without question the most common basic color is white. I expect that is because white and black go with "any" color and a black built up wing on a hot day can be a big problem (ask how I know if you're interested) so white is clearly the default base color for the majority although there is a good representation of black ones as well (including one of my first "pro" stunters).
Beyond those two I'd say that silvers of one sort or another were probably next most common and blues close behind. (Note, the vast majority utilized a large area of base color accompanied by a panoply of contrasting trim colors. In the US predominantly RW&B. Other countries seem to use a wide variety of trim colors on white bases, sometimes reflective of their countries flags and some not. A handful, such as the "purple" Walker Cup winner used a combination of a common "darkest" color brightened by the addition of a lightening base such as white, gold or silver for trim colors as appropriate to the darkest pigment.
There have been a number of bright colored winners over the years although multiple examples of Paul Walker and Dave Fitzgeralds' yellow/orange/candy/fluorescent versions might have spiked the percentage of same.
Re your "Camo" comment there have been any number of full camo paint jobs that flew to wins or very high finishes including those of Frank McMillan and Keith Trostle who specialize very effectively with such among others. there was one instance a couple of decades or so ago of an absolutely beautiful semi-scale Wild Cat that had a purposely "weathered" paint job that received very, very low appearance points because it wasn't shiny like the majority of the entries. After the appearance judging was over the shock of the competitors at the misdirected judge mentality that resulted in that score more than eliminated any chance that that low number (which doesn't appear on the judges' score sheets, by the way, but is added by the tabulators after each round) influenced maneuver scores from the flight judges.
So, for a very straight forward answer to your underlying concern I don't believe a cogent case could be made for any remotely verifiable color as the "best scoring" unless you wanted to say that, "obviously", it must be white because of its preponderance. Again, on my opinion that is primarily the result of pride of country and being a universally viable background for the flyer's favorite colors.
Finally, If you've anyone near to you or who might attend a contest in which you compete who has been a long time PAMPA member you be able to talk him/her into dragging along back "Nats" issues most of which have color pix of at least "The" Champ and, often, the top five and or all the class winners.
Hope this helps a bit.
Ted Fancher
With the exception of the obvious predominance of white base colors with a countless array of contrasting trims (albeit with the R,W,B noted above) I can't say that there is any "obvious" favoritism for "special" colors among those who were competitive in my active "career" (every Nats from 1964 through ~2007 plus judging a couple of years when Dave Fitz was the ED.