I Can't Have a Science of White Things

There are many categories that we form for which we cannot generate a scientific theory or explanation, precisely because those categories are not homogeneous. It doesn't mean those things don't exist. It means we cannot scientifically investigate them. For example, i can't have a science of white things. But the category i am using, this is j s mill's example, white things, does not support any inductive generalizations other than the thing is white. Now don't give me what we can have a theory about light and whiteness. We're talking about a theory about white things.