The answer really depends on how you define "having a color". The term "color" refers to visible light with a certain frequency, or a mixture of visible light frequencies. Therefore, the word "color" describes the frequency content of any type of visible light. Anytime visible light is present, we can describe it as having a certain color. With this in mind, there are many different ways an object can reflect or emit visible light. Thus, there are many ways an object can "have a color". While a single, isolated, atom can reflect or emit visible light in several of these ways, it does not participate in all the ways. If you define "having a color" very narrowly such that it only includes certain mechanisms, then atoms do not have color. If you define "having a color" more broadly, then atoms do have a color. Let us look at the different ways an object can reflect or emit visible light and apply each one to an atom