Well, sometimes there's white ice, and that's more obvious. But black ice is of course just clear ice, and it's the asphalt seen through it that's black. Nothing surprising so far, or even entertaining. But... what if this phenomenon were to occur between, say, Lake George and Round Mountain? Red ice, that's what!
Of course you are correct, but as a practical matter white ice never comes up when travel conditions are being updated. At least I have never heard it. I reckon it is just the vernacular, and is used reflexively.
More than white ice, black ice includes the "Oh s....t" factor when driver doesn't notice that black pavement has just changed to black ice.