I used to grab whatever cushions matched the chair and figure the sun couldn't do much damage in a season or two. Wrong, and expensively so. Three summers of bleached out stripes taught me that the fabric matters more than the color, and once I started checking for solution dyed acrylic instead of regular cotton prints, the whole headache went away.
Where these don't belong is anywhere damp and shut up tight, a covered box on a shaded porch where moisture sits and never dries out properly, or jammed against a stucco wall that holds heat and cooks the backing off the fabric over a couple summers. They also look wrong paired with anything too polished, a glass top table and chrome frame chairs make patio cushions look like they wandered in from the wrong room. Give them a plain painted rail, weathered wood, or a plastic resin chair and they settle in fine. As for wear, the good ones fade slowly and evenly rather than blotching, the fibers stay a little stiff for the first few weeks out of the bag and then soften up once they've had some sun and a few rainstorms on them. Mine get a quick hose down every couple weeks in summer, dish soap and a soft brush if a bird leaves a present, and I stand them on edge to dry so water doesn't pool in the seams. Left out from May through September here, mine held their color fine, no cracking foam, no mildew smell, though I did bring them in once for a monsoon that dumped two inches in an hour, because standing water is the one thing none of them recover from gracefully.
In an ordinary backyard, a couple of these on plain chairs next to a wood table does more for the place than a new grill would, and nobody walking out there thinks you spent a fortune, they just think you sat down and picked something comfortable. They sit fine next to a faded umbrella, next to bare concrete, next to a dog bed that's seen better days. Barbara put a set on the old metal gliders we'd had since Cleveland and said it was like getting new furniture for twenty bucks a cushion.
Press your thumb into the corner seam before you buy, if it springs back fast and feels dense all the way through, that's the one that survives a real summer out there.