The term “colour” in particle physics and quantum chromodynamics (QCD) refers to the property of quarks, which are elementary particles that make up protons and neutrons. Quarks can have one of three colours – red, green, or blue – and combine in different ways to form colourless particles such as protons and neutrons.
However, the concept of colour is not relevant to dark matter, which is a non-baryonic form of matter that does not interact with light or any other forms of electromagnetic radiation.
Dark matter is called “dark” because it does not emit, absorb, or reflect any electromagnetic radiation, including visible light. It is invisible to telescopes and other instruments that rely on light or other forms of radiation to detect objects.
While dark matter does interact gravitationally with other matter, it does not have any known intrinsic properties such as colour or electric charge. Therefore, the term “black” does not apply to dark matter in the same way that it applies to visible objects that absorb or reflect light.
In summary, dark matter does not have colour or any other intrinsic electromagnetic properties, and is called “dark” because it does not interact with light or other forms of radiation in the same way as visible matter.