Take me imagining a giant blue square. Some people would say, the arrangement of particles and energy in my brain is causing me to speak and act like I am seeing a giant blue square.
Now from their perspective I understand that, since they don't have my experiences of the giant blue square. But from my perspective, I am seeing a giant blue square. The giant blue square is the thing I am having direct experience of, and is the thing I can be certain, in that moment at least, that it exists. They can attempt to show me these particles and this energy, but in the end, whilst they certainly exist in some sense, I am seeing all this evidence in the same way I am seeing the giant blue square. As a conscious experience.
So, for all this evidence people have for the existence of a material world outside our consciousness, I can only see it as more conscious experience. I then don't see how logically, using only conscious experience, one can show the existence of anything but more conscious experience.
It seems futile to me, to try reaching outside of conscious experience, which encompasses everything we talk and think about, to talk about things outside of it.
Baring in mind that all science and empirical investigation functions identically, and is just as practical if we remember that it is all conscious experience we manipulate. In fact, given revelations about the world in the past 100 years, it may even function better if we remember that. Especially as more people begin investigating what consciousness is through empirical research beyond everyday experiences.
Summary: Everything I have ever witnessed is part of a conscious experience.