Interaction of Color by Josef Albers, a color app on iPad. Only available via US iTunes store for free.

https://itunes.apple.com/us/app/interaction-color-by-josef/id664296461?mt=8

If you want the physical book, Interaction of Color: 50th Anniversary Edition is available at Amazon (US | CA | UK | DE | FR | IT | ES | JP | CN) and Book Depository