"I just want this blue dress."
What's the explanation for why 蓝 here needs no 色 or 的 like colour words seem to in most of this course?
As a general rule when it's a noun you must add 色: "what color is your dress?" "红色" Also "descriptive" colors like 咖啡色 or 橘子色. But as an adjective it can be dropped; so you could say "他有红车" he has a red car. Or "他有红色的车" (he has a red colored car).