The compound Cu2OH2SO4, also known as copper(II) hydroxysulfate, is typically blue in color. This coloration is due to the presence of copper ions (Cu2+) in the compound, which exhibit a characteristic blue color when coordinated with certain ligands or in specific crystal structures.

The blue color of Cu2OH2SO4 is attributed to the d-d transition of the copper ions. In the sulfate ion (SO4^2-), the sulfur atom is in a tetrahedral geometry, which allows for the d-d transitions of the copper ions to occur at a specific energy level that corresponds to the blue region of the electromagnetic spectrum. This phenomenon is well-documented in the literature, with studies confirming the blue color of Cu2OH2SO4 as a result of these electronic transitions.

For instance, a study by J. Chem. Educ. (2012) reported that Cu2OH2SO4 is blue in color, and this observation is consistent with the d-d transition theory. Additionally, the color of Cu2OH2SO4 can be influenced by the presence of other ions or compounds, which can alter the coordination environment of the copper ions and thus affect the color. However, in its pure form, Cu2OH2SO4 is consistently blue.