* Atoms are too small to reflect light: Color is how our eyes perceive light reflected off of objects. Atoms are far too tiny to reflect light in a way that would create a visible color.
* Color is based on electron transitions: Atoms can absorb and emit light, but this is due to electrons changing energy levels. Hydrogen, with only one electron, emits specific wavelengths of light, primarily in the ultraviolet and visible spectrum (giving off a reddish-pink color in large quantities). However, a single hydrogen atom is not emitting enough light for us to see a color.
In short: While hydrogen can emit light and contribute to colors in larger quantities, a single atom is too small to have a discernible color.
