Adjectives follow nouns when you're distinguishing something from other things. As in, the red hats, as opposed to the blue hats. Saying "los rojos sombreros" sounds like you're saying that all hats are red, like talking about "la blanca nieve" (the white snow), that is, being white is an inherent property of snow, whereas being red is not an inherent property of being a hat.
In my country we only use the Spanish borrowing "sombrero" to define the Mexican type of hat, while there is a different word for the "hat" in general and several others for various types of hats. What I'm curious about is whether the people in Spanish-speaking countries have any specific word to refer to the Mexican sombrero as opposed to all others.
"I find the concept of giving attributes of an object AFTER the object to make a lot of sense even if it's completely strange to me as a native english speaker. Instead of say, "the red 4-door car" which in your mind you get something is red, then oh, it's red and has 4 doors, then finally, you figure out they are talking about a car with 4 doors and a red paint job. You get it's, "hey there's a car, and it's red with 4 doors". you get the object first then modify it in your mind instead of trying to figure out what they are describing before they tell you." -legere http://duolingo.com/#!/comment/85061