Naive realism is the common sense theory of perception. Most people, until they starting thinking philosophically, are naive realists. This theory is also known as “direct realism” or “common sense realism”.
Naive realism holds that the view of the world that we derive from our senses is to be taken at face value: there are objects out there in the world, and those objects have the properties that they appear to us to have. If I have an experience as of a large apple tree, then that’s because there’s a large apple tree in front of me. If the apples on the tree appear to me to be red, then that’s because there are objects in front of me, apples, that have the property redness; simple.
Plausible though naive realism may be, it has serious problems, among which is the problem of the variability of perception. The same object may appear differently to different people, or to the same person at different times. The apples may appear to be red in the daytime, but at dusk they are a shade of grey. If naive realism is to be taken seriously, and colours are out there in the world, then apples regularly change colour depending on how much light is around them. It is much more plausible, though, to think that the apples are the same as they ever were, that all that has changed is our experience of them.