I would say shape is relative. Any 'real' object's shape depends on the size of the measuring unit. A seemingly flat surface becomes quite irregular if you look closly enough. The closer the observer looks, the more it changes Maybe you can say the same about mass. Wouldn't an object have to have an effect on something else to say that it has mass? e.g. bend space-time. If so, mass is relative to its environment I think color & firmness are definately perceptions of an observer.