The scroll bar on that site is a cool way to represent the saturation. Scrolling with the mouse wheel changes saturation on http://colourco.de/ too, but it’s more obvious on the hailpixel site that you can use the mouse wheel.

Do either of these "intelligently" pick colors? Just playing around with them, it seems I can't make anything ugly.

I prefer this site. clearer and simpler, focus, than http://colourco.de/

Try code mode.

Sort of, but providing the scheme progressions is really neat.

any idea how this guy calculated the colour for the text dynamically so as to maintain the contrast difference?