Direct calque of European 'rose-colored.' Like English 'rose-tinted glasses,'
玫瑰色 carries a figurative sense of unrealistic optimism — especially in
玫瑰色的梦 'a rosy dream' or
玫瑰色的幻想 'rose-tinted illusions.' For the literal flower color,
粉红色 (fěnhóngsè) 'pink' is more everyday.