Euphorbia enopla is admired for several features including the conspicuous long spines. On new growth the spines are dark pink to reddish. They later turn darker, becoming a series of shades of purple or a blackish maroon. Eventually they dry out and become grey as in the picture which was taken in the summer with the plant in rest.
The plant resembles E. ferox that has thicker stems (www.cactus-art.biz).