All that glisters is not gold. or All that glitters is not gold.
Meaning: "An attractive appearance may be deceptive. It may cover or hide a much less favourable content."
Source for meaning: Paczolay, Gyula (1997). "19". European proverbs: in 55 languages, with equivalents in Arabic, Persian, Sanskrit, Chinese and Japanese. Veszprémi Nyomda. p. 125.
Ward, Caroline (1842). National proverbs in the principal languages of Europe. J.W. Parker. p. 114.
William Shakespeare, The Merchant of Venice, act II, scene 7.