Red, white and blue is quite common on flags. Navy suits are often worn with a white shirt and a red tie.
Red and blue don’t mix though; they are neither analogous nor complementary colors. It’s like matching purple with green or orange with purple.
Why is it so common and accepted then?
Red stands out, but some people would say that it stands out too much, and a flag that is mostly red would be too gaudy. Navy or royal blue is a bold color, but it isn’t gaudy. And white adds some light tone to the combo. Red, green, and white are also a very popular combo.
Red, White, and Blue are the American colors. Obviously they are exceptional!
While it’s obvious you’re being facetious here, it’s worth noting their popularity predated the US. Notably, post-revolution France and the Great Britain used them.
You’re right about GB (1707 at least), but umm… the US (1777) had its revolution and flag before France (1791, pre-revolution).
Many places, such as Puerto Rico and Liberia, are consciously copying the US. And many more current/former Commonwealth nations use parts of the UK flag.
P
Is not! (Link.)
Plus there’s oodles of RWB tricolours in the Slavic countries, including the flag of Russia!
FWIW, the red, white and blue scheme of the Union Jack has more to do with politics than aesthetic appeal. That combo just happens to be what you get when you combine the Scottish and English flags.
Part of it might have to do with the biology of colorblindness. Red and blue are distinct colors to almost everyone. Even for people with a total lack of color vision, white can be distinguished from both blue and red, just because white is so much lighter than blue or red.
There might also be some history to it. Blue and red are both colors that people have been able to dye clothing for a long, long time… As a result, blue and red are both relatively traditional colors to wear, along with black or “natural” hues.
Some shades of purple and green, by the way, go very well together. Deep purple and forest green were a popular color combination for women in Europe in the 19th century. That color scheme showed up again a year or two ago in the Gap’s line of summer and fall clothing, IIRC.
While there’s no official symbolism behind the colors on the US Flag, apparently there was in the Great Seal.
With a name like yours, cmyk, I was expecting a thorough color analysis! 
It’s Saturday, he’s probably off-duty.
Flags aren’t made with fashion in mind. They are made to be striking, bold and visible. The strong primary colors of red, blue, yellow and green (along with black and white for definition) do that very well.
You can click through the World Flag Database and see very little orange and teal along with a few “off” colors that I don’t even know what to call. Countries probably don’t want to be represented by flags whose colors are difficult to classify (is that light blue or teal on Fiji’s flag?).
As for suits, I’ve always hated navy because it’s too dark to be blue but not dark enough to be black. But it’s dark enough that a red “power tie” doesn’t fight it that much.
He’s cmyk, not rwb. 
The only way the Canadian flag could be gaudier is if it had gold and not white. No offense.
Cyan, magenta, yellow, and black are the “primary” colors of ink.
But those are used for the “four-colour” printing process, building up other colours from the primaries. In flags, we are generally dealing with “spot” colours using inks or dyes of specifically-chosen colour. Hence, rwb.
In the days before synthetic dyes, madder (which makes red) and indigo (which makes blue) were relatively affordable natural dyes which made clear and durable colors. That would also have been a consideration. You don’t want a flag that fades too quickly in the sun or with colors that run when it rains, and you don’t want the flag budget to bankrupt your army.
The same thing probably also helps explain why the combination is so common in clothing - it’s traditional, from the days when red and blue were colors the common folk could afford.
The Dutch flag started in the 16th centrury as orange, white, blue. Mid 17th century the orange was replaced by red (vermillion, actually), either because the yellow dies in the orange faded, leaving red - or to make the flag bolder. Regardless, this being the oldest tri-color in continuous use, al the otah haters are just imitators. This color combo pre-dates above mentioned France, Russia, UK and U.S.
So then the combo comes from the livery of the Prince of Orange, adjusted to allow for different fading characteristics of various dies, or just because it looks good flying from a ship.
There’s no “rule” that only analogous or complementary color schemes can be used.
Sure, there’s no law against it. You only have to fear punishment from the fashion police.
