redden in WordNet English dictionary

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