The Collaborative International Dictionary of English v.0.48:

Redden \Red"den\ (r?d"d'n), v. t. [imp. & p. p. Reddened
   (-d'nd); p. pr. & vb. n. Reddening.] [From Red, a.]
   To make red or somewhat red; to give a red color to.
   [1913 Webster]