Word / formMeaning / explanation
اِحْمَرَّit turned red.
يَحْمَرُّit turns red.
اِحْمِرَارًاbecoming red.
مُحْمَرٌّbecoming red.
اِحْمَرَّturn red!
لَا تَحْمَرَّdo not turn red!
This verb is generally intransitive. It must not be confused with the causative حَمَّرَ “he reddened something”: becoming red and making something red are different events.