I just had a debate with my roommate who wouldn't agree that a color is an abstraction. I tried to explain to her that a property standing by itself is an abstraction, things that possess this property can be concretions. She would say "color is a wavelength" to which I answered wavelengths provide sufficient and necessary conditions as to when we perceive a certain color, but the color red itself, in other words the property "redness", is an abstraction. She finally ended up telling me that we have different definitions of abstraction and left at the debate at that. She told me that in my world "everything is an abstraction" which is obviously a gross oversimplification. But I did tell her that, for example, what makes a table a table, in other words its defining properties, as seen by themselves, is an abstraction. She didn't provide any convincing argument as to why I'm wrong, but if you can, by all means do.