My suggestions would be a quilt with a neutral background i.e. white, grey, etc., and pops of colour in the design. For me, a quilt with colour throughout and no neutral colour would be more difficult to fit into a particular colour scheme. Size wise, my suggestion would be a large lap quilt i.e. small enough to move around the house for cuddling under but big enough to fit over a single bed or folded on the bottom of a double bed for pulling up. I have added links below to the kinds of quilts I would buy tickets for.
http://www.diaryofaquilter.com/2016/...-patterns.html
https://beechtreelanehandmade.com/20...d-scrap-quilt/
I wouldn't buy a ticket for a very traditional quilt, a quilt with a theme i.e. cats, hearts, etc. or a quilt with a very definite colour scheme. Just my thoughts. Good luck with your raffle quilt! I'm sure it's going to be awesome and please share when it is finished.
