it could be frank color smirking through, or just a hard to describe graying of the new color.
It could be the button depressions, a vague emptiness or hollow over a concave area that changes the color or surface appearance. " Innies "
It could be the cord of the upholsterers work that is rigid and leaving a bump. " Outties "
It could be the contour that the slipcover cannot adhere to, the the difference, for example, a serpentine deck front, you can just " see " it underneath.
For that matter, arm pits that scream at you that it's isn't sticking like paint.
Can we size this up in one phrase or word, the absence of all the things that a slipcover look less than sucessful ? Can we find a word that says what the most sucessful slipcover does ?
( without my usual circular uneditted encyclopeadia answers ).