苍 (cāng) is a bound morpheme (b.f.) that rarely stands alone in modern Mandarin. It appears mainly in literary or classical compounds expressing colors (dark green, blue, gray, ashy) — like 苍白 'pale' and 苍天 'the blue heavens' — or in words describing aging (苍老 'aged'). It's also a common surname (Cang). Because it's a bound form, you'll encounter it as the first character in disyllabic words or in chengyu, never as an independent word.