The solid form of HGO, or hydrogen gas, is colorless. This is due to the nature of hydrogen gas itself, which is transparent and does not absorb or emit light in the visible spectrum. The colorless nature of HGO is consistent with the properties of hydrogen gas, which is a diatomic molecule (H2) and does not have any color. This information is supported by various scientific sources, including the National Institute of Standards and Technology (NIST) and the Linus Pauling Institute at Oregon State University. These sources confirm that hydrogen gas is inherently colorless, and thus, HGO, being a solid form of hydrogen gas, retains this property.