I've always used Sunbrella outdoor fabric and never had a problem.

I have almost always had offwhite cushions on my porch furniture, and my porches were used year round so they were never stored. They were regularly washed. I agree sunbrella is a good choice. Im planning to do off-white again on our new porch.

I love color for outdoor furniture and often colors you would not do inside so bright and multi colors . I have multi colored print on outside furniture it is 17 yrs old and I wash the covers maybe every 2nd year thay are really good quality covers made from sunbrella fabric still look great and have handled the odd wine spill or chocolate cake smear . I think light colored no print cushions are boring but I gess if you must then make sure what you get are washable and weather proof Mine are also stored in a outdoor cabinet in the winter and no issue there ,