The first thing I do is pinch the corners. A neutral pillow lives or dies on its shape, and if the corners are floppy and sad right out of the package, that pillow is going to look tired in a month, not a year. I want a corner with some structure, a seam that holds, and a cover that feels like it has weight to it, not like it will go limp the second someone leans back with a cup of coffee.
What separates a good one from a disappointing one comes down to what you can't always see in a photo. A linen or a cotton linen blend with some texture to it reads as calm and a little expensive, even when it wasn't, while a shiny polyester cover reads cheap no matter what you paid. Flip it over and look at the zipper, a hidden zipper in a proper seam means someone thought about this pillow actually living in a house, while a zipper stitched crooked along the edge is a sign the rest of the construction probably got the same amount of care. The insert matters just as much as the cover. A thin, flat insert stuffed with the cheapest filling will go pancake shaped within a season, and no amount of fluffing brings that back. A better insert, down or a good down alternative, keeps its loft and keeps bouncing back after someone sits on it, which in a real living room happens constantly.
In an ordinary room, neutral pillows are the ones that let everything else do the talking. They sit well against a patterned chair, a colorful throw, a rug with some personality, because they're not competing for attention, they're just giving your eye somewhere to rest. The mistake I made for years was buying too many at once, all the same size, all lined up like soldiers across one sofa. Two or three in slightly different sizes and textures look like a room, a whole matched set looks like a showroom display nobody's allowed to touch.
Over time, a well made neutral pillow softens in a good way, the fabric relaxes, the cover gets that slightly worn in look that actually suits neutral tones better than bright ones. Covers with zippers are worth it because you can pull them off and wash or spot clean them, which matters more than people expect once a pillow has lived through a few seasons of actual use. I just give mine a good fluff and a punch in the middle most days, and a wash when something spills, which it will.
Measure your sofa or chair cushion before you buy, and size your pillow a few inches smaller than that so it doesn't look like it's trying to take over the seat.