pinyin: cǎi

Chinese phrase: 采茶 cǎi chá - pick tea
采用 cǎi yòng - adopt

Examples:
菜
pinyin: cài; meaning vegetables
Chinese phrase: 洗菜 xǐ cài - wash vegetables
点菜 diǎn cài - order dishes

彩
pinyin: cǎi; meaning colors of all kinds
Chinese phrase: 彩色 cǎi sè - colorful, many colors
精彩 jīng cǎi - wonderful