Why do pianos have black and white keys?

Answer: Shows sharps/flats vs natural notes

Cheaper to make two colors only — Wrong. The two colors serve a musical purpose, not economic. They help distinguish between natural notes and sharps/flats.

Shows sharps/flats vs natural notes ✓ — Correct! White keys represent the seven natural notes (C, D, E, F, G, A, B) in Western music. Black keys are the sharps and flats between them. This visual pattern helps pianists quickly identify notes and navigate the keyboard without looking.

White keys play melody only — Wrong. Both black and white keys can play melody or harmony. The colors indicate note type (natural vs sharp/flat), not musical function.