“yellow” in Japanese is 黄, read ou, kou, ki (おう, こう, き). It is a Grade 2 Kyōiku kanji, taught in year 2 of Japanese elementary school, and appears in words such as 黄色 (yellow color).
What does 黄 mean?
黄色い花がきれいだ。
Same sound, different character — the classic trap. Compare them side by side: