Translation:She wears a red sweater.
What you can do with all colors (using them as no-adjectives):
What you can only do with i-adjective colors (I think around 7 in total):
I think putting 色 after the color is optional. You see it sometimes, but not all the time.
紫色のズボン = purple-colored trousers
紫のズボン = purple trousers
Some colors do have the 色 in them, like 茶色 or 黄色. Those are not optional of course.