saw at airport:
it would be sweet to do with CSS blend modes so you could multiply the colors together, but I don't think it's going to happen: http://codepen.io/chriscoyier/pen/uBcKh blending only works on multiple backgrounds not arbitrary elements. Maybe could do with SVG though.
Update! works with
mix-blend-mode (in Chrome Canary with experimental web platform features turned on) :: http://codepen.io/cjgammon/pen/nEzpj