It's difficult to tell what they'd have actually looked like as a finished result. Like the other poster said, what we have are traces of base coat pigment, and to speak from a modern sculpting/painting standpoint one often needs to use too bright colors in the lower layers to get the correct color in the upper layers.

I think what the final result would look like would probably depend on where a statue was going to be displayed: the Romans had a very limited toolkit to work with so far as paints went, and the ones that would hold up to outside weather were kind of shitty and ill-suited to fine detail work, so a statue displayed in a square would probably have less detailed and realistic paint work because it just wasn't possible and it would probably have to be regularly touched up or repainted anyways. A statue displayed inside may very well have been genuinely lifelike, because judging by the comparatively small number of true paintings that have survived from that era they had both the technical skill and the materials to do so.

That means an outdoor statue may well have looked like that picture, while a statue in a villa may have looked more like one of those really uncanny wax sculptures.