Yup you can do it all year. If it snows where you are the snow will deflect the sun so I know on white items they get really white. I have accidently left things on the line for days at a time and they ended up faded so just remember where you put the clothes :LOL .
My girlfriend swears by Cascade. You have to get the creamy liquid kind & scrub it a little with a small brush (old toothbrush would work), but she says it gets out all protein stains. I haven't tried it yet, but thought I'd mention it.
Hey Goldie........ I tried the sun thing today and holy cow it is like magic you can literally watch the stains disappear poof they are gone I only left them out there for an hour and everthing was pretty again.