This question, and the SE policy that Monica points to, misuse the word subjective in a way that is all too common today. Objective means that you are describing the characteristics of the object. Ice cream is made with milk. Subjective means that you are describing the properties of the subject. My favorite ice cream is maple walnut.
There is always an objective property to which there is a subjective response. A person can both recognize the objective property and experience a subjective reaction to it. They are not two different properties, therefore, but two different perspectives on the same property. The car is red. I like the car because it is red.
If the subjective response does not correspond to an objective property, then it is not a response at all, since if there is no objective property there is nothing to respond to. It is not a response, but an illusion.
If we say that a certain book or poem is "great" therefore, there is both an objective property and a subjective response involved.
The difficulty here is not whether the objective property we are referring to is objective, it is whether it is countable. The scientific bent of our age has led us to look for ways to count the properties of objects. This practice has greatly increased our ability to agree on the exact properties of objects and to manipulate those properties in particular ways. But it has also led us to discount any property that we cannot find a way to count. If a property is not countable, we tend to dismiss it as not real, and in so doing we tend to dismiss it as "subjective".
One of the advantages of this approach to countability of properties is that it allows us to recognize that some people have defective perception. We can count the wavelengths of light emitted by a red object and thus definitively say that if a person cannot tell red from green, this does not make the redness of the object a "subjective" opinion, it means that the subject has defective color vision. Their view that my red car is actually green is "subjective" in the sense that it is a property of their vision, but is is also a demonstrably false response to the objective redness of the car.
Our ability to count aesthetic properties such as beauty is very limited. (It is not non-existent, there is the golden ratio for example.) Does this mean that these properties don't exist or does it simply mean that we have not learned to count them yet (or perhaps that they are inherently uncountable)?
Requiring that a property must be countable to be considered real is really just a methodological prejudice. We have a useful method for dealing with countable things, so for purposes of that method we only look at properties that we have figured out how to count. But does this prove that the other non-countable properties do not exist? Certainly not; countability is just a requirement of the method, not a criteria for existence.
So, if we allow that non-countable properties, such as beauty, can exist, then they are objective properties of the object. The waterfall is beautiful is an objective statement about the waterfall.
It follows that if a person looks at the waterfall and fails to have the subjective experience of appreciating its beauty, it is not because the beauty of the waterfall is "subjective", but because it is an objective property that the subject cannot see, just as the color blind subject cannot see the objective redness of a red car. The subject's aesthetic sense is defective, just as the subject's color vision is defective if they don't see the red car as red.
The subject's seeing the waterfall as ugly and the car as green are both subjective responses which are false to the objective properties being observed. But the objective properties have to be there in order for there to be a subjective response to them. If the color is not there at all, the subject's response of seeing red or green are both equally illusory. An illusion is a subjective response where no corresponding objective property exists.
To call any aesthetic property "merely subjective", therefore, is actually assert not that it is subjective (you see green even though the car is actually red) but that is is illusory (you see the waterfall as beautiful even though there is no such thing as beauty).
You may, of course, give in to the methodological prejudice that only countable properties are real. In that case, you should call uncountable aesthetic properties illusions, not subjective. If you allow for the existence of objective aesthetic properties, though, then you should recognize that an individual subject can have defective aesthetic sensibilities (which may or may not be correctable) and that their subjective response to a beautiful object (or an ugly one) may be more or less true to its objective aesthetic properties.
If objects can have objective aesthetic properties, though, then we can ask factual questions about them and give factual answers about them. Those properties may be uncountable, and therefore the answers to questions about them may be harder to demonstrate or to prove, but that does not prevent them from being factual. For that matter, we should note that countable properties could be illusions just as much as uncountable ones.
