The Collaborative International Dictionary of English v.0.48:

Empurple \Em*pur"ple\, v. t. [imp. & p. p. Empurpled; p. pr. &
   vb. n. Empurpling.] [Pref. em- + purple. Cf. Impurple.]
   To tinge or dye of a purple color; to color with purple; to
   impurple. "The deep empurpled ran." --Philips.
   [1913 Webster]

WordNet (r) 3.0 (2006):

empurple
    v 1: color purple [syn: purple, empurple, purpurate]