The technique used in the excerpted lines is simile. Option C is correct.
Simile is a figure of speech that makes a comparison, showing similarities between two different things. Unlike a metaphor, a simile express resemblance by employing words such as “like” or “as
In this particular case the simile refers to: "... blue as blood [as his left forearm] ..." . The author is usisn the word " as" to make the comparison.