They're on opposite sides of the color wheel, so they contrast and look really good together, blue and orange, yellow and purple, green and red are all complementary colors. It's like how black and white work together. Complementary colors are what makes a sunset look incredible, the blue sky with an orange glow. I have no idea what thatguy is talking about.
Here's an example of a color wheel. Each primary color has a secondary color that complements it and the tertiary colors are opposite each other. It's color science.