I contacted the Marble Institute of America (I think--it's been awhile), about oiling honed black marble to enhance the color, rather than using a color enhancer or an impregnator (sealer). Someone emailed me that either would work, but to use mineral oil--not vegetable oil--to avoid the rancidity issues. I experimented on pieces of marble, but the oil seemed to evaporate very quickly, so I eventually used the impregnator on the black marble, and I am happy with the darker color. I use a marble polish containing silicone/dimethicone on the black marble when I want it to look especially smooth, silky, and pretty for company.
My carrara marble is honed, hand-polished, and not sealed. I often roll pie crust, biscuit dough, puff pastry, etc. on one end, and have not noticed that it looks saturated. I've even kneaded bread dough by oiling the counter first. My carrara has a lot of gray in it, but the white area on that end is just as white as the rest of the top.
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Unsealed marble
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