For Day #292 of the 365 Days of art, I have some blue and orange....
Each primary color (red, blue, and yellow) has a contrasting "complementary" color that makes it stand out more. The complementing color is what you get by mixing the other two primaries (red + blue= purple; blue + yellow = green; red + yellow = orange).
The pairs are red and green, purple and yellow, and blue and orange.
Today we have some blue and orange and when complementary colors are placed side by side - they become more VIVID - stand out more - so they are good for signage, logos, or times when you desire contrast.