Perception is an extremely subjective interpretation of inputs that may or may not involve the I- function as a contributor to the subjectivity, but it depends on the kinds of inputs that the nervous system can receive, i.e. on the kinds of sensory receptors that the nervous system has incorporated into its repertoire. Thus our interpretations of reality are ultimately based on the kinds of information that our sensory transducers can introduce into our nervous systems. The kinds of receptors that organisms possess, and their level of functioning usually remains fairly constant within species, but some variations may be seen. Thus amongst humans, most people can see all three primary colours of light, and myriad of colours formed by combination, but some cannot, and are hence "colour- blind". Colour- blind people's view of reality hence must be vastly different from that of "normal" people.
As far as depth perception goes, it is based on the accommodation abilities of the lens and its adjunct ciliary muscles and suspensory ligaments, and the ability of the brain to monitor the intensity of the image on the retina of BOTH eyes. If one eye is closed, or not involved in the depth perception process in some way, it becomes much harder to estimate distances. Thus both eyes are obviously necessary for the correct functioning and interrelations of the brain and retinal signals. But this observation then raises the question as to how much more input does the brain have into the final picture of the object that we carry in our heads, distinct from the image of the object on the retina?
Using the above observations coupled with those from blind- spot tests, it can be seen that the brain provides a significant portion of the picture of "reality", implying that nothing, then, in terms of how we see the world, is absolute. There can be no standard against which to compare differences, at least in terms of those components of the entire picture that do not use input from other sensory transducers. Thus shape may be considered to be reasonably accurately detected by the tactile senses, as can be texture and temperature. But there does not seem to be any way to absolutely compare components such as colour, which depend purely on the visual senses, leading to highly subjective descriptions of colour.
Everything is "subjective", for the reasons you give. At the same time, also for the reasons you give, it can become more and more "objective", by checking the "reality" using other senses, as well as by trying to understand how the same things are felt/seen/understood by other people. In the last analysis, though, you are right, that we like an absolute standard by which to evaluate the veracity of our pictures. That ok? PG