Unless the people attending the auction are quilters/sewers/crafters, they do NOT understand the amount of time & money that goes into something handmade. As several other people said, at most of the silent auctions I've attended, the quilts go for WAY less than the value of even the materials. Our guild used to donate quilts for benefit auctions, now we stick to smaller items like table runners or seasonal wall hangings.
The exception may be if the item being auctioned somehow ties into the 'theme' of the benefit - my friend was trying to raise money for a restoration village that has a threshing jamboree each year, including a tractor parade. In the year that John Deere tractors were being featured, she made some John Deere quilts, and of course those brought in better money. Or if the benefit is for Ducks Unlimited, a duck quilt might be a hot item.
How about combining a runner with a matching candle? Or a set of placemats & napkins, then find some matching napkin rings? And I believe seasonal things sell better than a specific color - if you make something blue, it may not match anyone's house. But mostly everyone will decorate for Christmas or Thanksgiving/autumn or Spring.
Andi