Colorado Bike Laws require the USE OF LIGHTS and it makes good sense to make yourself as visible as possible to cars and trucks. If you are riding between sunset and sunrise, cyclist must use lights. The law specifically requires that a light system for bicycles must, at a minimum, include a white light that is visible from five hundred (500) feet to the front and a red reflector on the rear that is visible from all distances from one hundred (100) feet to six hundred (600) feet when directly in front of lawful low beam headlights. (C.R.S. 42-4-221). We like the flashing white lights on the front of your bike with a brightness of at least 50 lumens. For the rear of your bike, we like a flashing red light of at least 20 lumens, and the more lights on the rear of your bike the better and more visible you will be to drivers. If you want to add a blue or yellow light to the rear of your bike, we think that is a good idea and there is no current Colorado law against doing that, and we advise bike riders to wear reflective clothes make themselves as conspicuous and safe as you can.