I wouldn't usually worry about the color scheme. There is only one case I know of where color scheme was involved in a legal case & upheld. The tricky part is whether you/the charity can sell a quilt based on someone else's design without their permission. You'll find loads of discussions on this topic here on the board. Honestly, there just isn't a whole lot of legal precedent so designers claim their designs are protected & people who use those designs without permission claim they aren't. To be clear, if a design were to be covered by copyright/patent, the US Fair Use law states "Acknowledging the source of the copyrighted material does not substitute for obtaining permission." An IP attorney could best advise you on the issue. To avoid all the controversy, I always make sure to get permission from the designer before using either a design or a pattern to create a quilt I either plan to sell or give to charity for an auction. That may be overkill, but it's what I do.
And by the way ... I think it's wonderful if you also want to notate the sources of your inspiration. Just because it isn't necessary, doesn't mean it isn't nice to do.
