QCD stands for Quantum ChromoDynamics. It is the current theory that talks about Quarks & Gluons, which are the building blocks for protons and neutrons. I think it talks about other particles also.

The physicists who developed it are some what whimsical. They talk about properties like strangeness, color, up, and down. So you can have a strange blue up quark.

The words have very little to do with the properties. They were chosen arbitrarily to suggest that the properties cannot be modeled by classical world properites.

Quantum theory is difficult to understand because our brains have been trained to cope with the classical world of our senses. Over a million years of evolution has hard wired certain perceptions and ways of thinking into our minds. The quantum world is so different from the classical world that we are just not equiped to understand it.

Visualizing and understanding the quantum world is like trying to visualize and understand 4D objects. We can write equations and calculate volumes, but we cannot visualize the corner of a hypercube.