THe suggestions above should render a dark-enough color.
Remember that the upperworks are a very pale gray, and not white. The contrast will look white or near-white but that scales poorly, typically.
You will probably want some pure white for the turret tops, the better to render the red paint upon them.
You will want some "range" in the dark gray, too, the better to pick out details, gun mounts and the like. Dark colors are a bear to model without becoming monotonous.