I have black goretex rain pants I wear when it rains hard or is daylight.  I got these to wear at night or when caught out in a shower.  The pants are very light weight and come with a pouch, so I keep them in my panier and it doesn't take much room.  I can pull the pants on (carefully) over my bike shoes, and use an ankle strap to gather the surplus material.  As a driver it amazes me to see serious bikers on high end road bikes dressed in dark clothing at night.  I may be imagining, but when I wear my radioactive yellow jacket and pants, drivers give me a wider berth.