reddening

(verb) turn red, as if in embarrassment or shame. Synonyms: blush, crimson, flush, redden. Example: "The girl blushed when a young man whistled as she walked by."

(verb) make red. Synonyms: redden. Example: "The setting sun reddened the sky."

(verb) turn red or redder. Synonyms: redden. Example: "The sky reddened."