"The orange flower is cheap."
Translation:주황색인 꽃이 싸요.
It's a pronunciation thing. Color words in Korea are really annoying because there are a hundred ways to say "red." The verb form of red is 빨갛다. You've probably seen it as 빨간색. 색 alone is color, so 빨간 is the adjective. The important thing though is that it's easy to make 빨갛다 an adjective with the -ㄴ sound. Same with 하얗다 => 하얀. 하얀 호랑이, 빨간 여우. With 주황 it would need to be 주환. 주환 신발 sounds really strange. 초론 사과 sounds weird. That's why for certain colors they add -색(인).
In most cases, it's best to just encounter it over and over again, instead of pure memorization. That's why it's good to have a language partner if you can find one. You will see the language used naturally often and will have natural conversations, so you can find your voice while figuring out grammar rules.