Answers: Colorado is a very low allergen state. Since it have low humidity, dust mites and mold are not as big an issue with Colorado. Colorado will still own issues with season allergies resembling grasses, trees, ragweed. Washington is humid so mold and dust mite allergy sufferers may suffer more there as ably as tree , grass and rag weed allergies.
I've never be to Colorado but Washington is a difficult place to live for allergies theirs lots of weeds, grasses, trees and animals that you can receive sick from I mean it depends on where on earth you live and what your allergic too, also in Eastern Washington here is alot of farming but it's so dry over near im sure theirs resident areas where not much follage live.