Painting rainbows in watercolor

Somebody in my class asked me a couple of weeks ago how to do this. Not that it's a great idea, because rainbows are so variable and tend to look hokey in your paintings, unless you happen to be J.M.W. Turner. Nevertheless, yesterday I showed them a way to do it in watercolor just by blending clean, diluted pure colors on slightly damp paper. It isn't hard to make a rainbow, but to put one in a painting and have it look realistic is a whole different thing. That takes practice. My first recommendation is to Google "rainbows" and see what they really look like. Most of them aren't complete. The colors are brighter near the ground, then they often disappear before the arc is completed. And red is always at the top, with violet at the bottom (and often hard to see). If there's a second rainbow reflected above it, the colors are reversed. And just in case you learned ROYGBIV when you were in grade school, there is no "I" for indigo in the spectrum, therefore it's actually ROYGBV. Newton must have been having a mystical moment when he described the colors--had to have seven, as in the days of Creation and notes on the musical scale.