Here's the wall before the stripes - the room is painted in Navajo White from Olympic, a great low-VOC paint from Lowes.
We wanted about 4 or 5 colored stripes on the wall, plus equal-sized "negative space" with the wall color. So based on that and the wall height, we went with 10 inch wide horizontal stripes. I used this great tutorial from Young House Love as our guidance.
The stripe color is a custom match of Benjamin Moore's Woodlawn Blue in Olympic paint from Lowes. Gotta love that they have the colors for designer fan decks in their computer.
AFTER - daytime