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]

The Collaborative International Dictionary of English v.0.48:

Redden \Red"den\, v. i.
   To grow or become red; to blush.
   [1913 Webster]

         Appius reddens at each word you speak.   --Pope.
   [1913 Webster]

         He no sooner saw that her eye glistened and her cheek
         reddened than his obstinacy was at once subbued. --Sir
                                                  W. SCott.
   [1913 Webster]

WordNet (r) 3.0 (2006):

redden
    v 1: turn red, as if in embarrassment or shame; "The girl
         blushed when a young man whistled as she walked by" [syn:
         blush, crimson, flush, redden]
    2: make red; "The setting sun reddened the sky"
    3: turn red or redder; "The sky reddened"

Moby Thesaurus II by Grady Ward, 1.0:

50 Moby Thesaurus words for "redden":
   blanch, blush, carmine, change color, color, color up, crimson,
   darken, flame, flush, frown, glare, glow, glower, gnarl, grow red,
   growl, henna, incarnadine, inflame, lipstick, look black,
   look daggers, lower, madder, mantle, miniate, pale, pink, red-ink,
   rose, rouge, rubify, rubric, ruby, ruddle, ruddy, rust, scowl,
   snap, snarl, spit, squirm with self-consciousness, stammer,
   turn color, turn pale, turn red, vermilion, warm, whiten