Philosophy: Reality?

I believe that universal reality cannot be simply grasped by human consciousness. If I have to choose a side between realism and positivism, the following statement would make one think that I am a realist, but I also have some skepticisms about the “universal reality.” Although I do believe that seemingly universals exist in this world, at the same time, I also believe that our mental experiences can shift what seems to be ‘universal’ to a mere illusion; ‘blue pencil’ might have the form of ‘blueness’, but some others might not perceive the ‘blue pencil’ having the form of ‘blueness’. What I believe to be sure is that the difference between the above example is definitely cultivated through our mental process; one’s illness can be the case that some cannot perceive the form of blueness in the ‘blue pencil’; if one had never seen the form of ‘blueness’, he/she would not possibly think or say that the pencil is blue; while the majority of people would perceive blue pencil as having the form of blueness.