I learned while we in Ireland earlier this month that the Irish flag expresses a hope for peace between Protestants and Catholics.  Orange is a color that has been associated with Protestantism every since William of Orange defeated James II at the Battle of Boyne in 1690.  Green has represented Irish republicanism since March 7, 1848, when it was flown over the Wolf Tone Confederate Club in the city of Waterford by Thomas Meagher. 
I love the idea of a white band representing peace between the parties represented by the other colors on the flag. I would dearly love to have peace in my country again and I would be willing to propose a flag where red, representing the Republicans, and blue, representing the Democrats, would be kept apart by a band of white, representing peace. There is the small difficulty that such a flag is currently the flag of France. This echoes George Washington’s criticism of Betsy Ross’s flag–according the Stan Freberg’s history of the U. S.–“The same as the Brit-ish colors, too.”
We could try to finesse our way out of it. Here is the flag of France. The blue band is on what they call “the hoist side.” According to my quick review of the flags of the world, there is no flag with these colors in this alignment where red is on the hoist side. That would make the new U. S flag unique in the very narrow sense of the word, but you would have to look really hard to see which nation is being represented, and that’s not a good thing for a country’s flag. 
Maybe we could superimpose the Statue of Liberty on the white band. That would put “liberty” and “peace” on the same band and would serve as an apology to France for stealing their flag in every but the most technical of senses.
The colors as representations of the Democratic and Republican parties ave very recent as the accompanying chart shows. The names of the parties have been with us for a long time, of course, although Jefferson represented the Democratic-Republican Party and Lincoln the Republican Party. 
If the flag were to represent liberals and conservatives, it would be representing words that have been with us for a long time, even though the meanings of the words have varied with the times. If the flag were to represent left leaning and right leaning parties, it would, again, be using words that have been with us for a long time—since the French Revolution, in that case.
Still, “red” and “blue” are now stable political designations and hope for peace between them belongs in the same league as the hope for peace between Irish Protestants and Irish Catholics.
 A Wikipedia article uses the word “truce” in place of “peace,” but I think that if we are going to see the flag as aspirational, we might as well go for the more lasting meaning.
 Just why we use the word “orange” is a long and twisted tale going back to the name of a water god in southern France. It is too complex even for a footnote, but I recommend http://www.squirrelbasked.wordpress.com. Search for “orange” and choose the article called “Words: orange in not only a fruit.”
 Green as a color representing Ireland is said to go back to St. Patrick and is supported by the designation “the Emerald Isle” because of it vibrant green color.
 And don’t think you can just change the direction or the order of the stripes. All those have already been taken, most prominently by Russia.
 Andrew Jackson was the first U. S. President to be simply “Democrat.”