Derived from

Basic 32x32 sci-fi tiles for roguelike
by Stephen Challener (Redshrike) and Daniel Cook, hosted by OpenGameArt.org
http://opengameart.org/content/basic-32x32-sci-fi-tiles-for-roguelike
http://creativecommons.org/licenses/by/3.0/
http://opengameart.org/content/oga-by-30-faq

Colored Metal tiles 1b
by sgtcrispy
http://opengameart.org/content/colored-metal-tiles-1b
http://creativecommons.org/publicdomain/zero/1.0/