baby blueEnglishOxford Dictionary of Englishbaby blue /ˌbeɪbi ˈbluː / ▸ noun 1 [mass noun] a pale shade of blue: she always wore baby blue to match her eyes [as modifier] baby-blue and pink streamers. ▪ (baby blues) informal blue eyes: O'Toole's famous baby blues are sparkling with mischief. 2 (baby blues) informal postnatal depression.