An alternative explanation might be that one person removed the wheels and a different person put them back on. It is possible that the person who put the new black steel rims on grabbed black nuts that were actually from another car thinking they were correct because the color matched. I don't mean to apologize for any tire place - I've never had a good experience with one, but there is a reasonable explanation that does not include malfeasance. Still insist that they replace them. Also, show them your alloy 26-spoke wheels, since they are much "nicer" and it is more reasonable to conclude that chrome nuts were used on the fancy alloy rims. Furthermore, it is possible that the black nuts are not quite long enough for the alloy rim hub caps to grab on to. I would check that carefully if you end up stuck with the black lugnuts. Those hubcaps are generally expensive so you don't want them to fall off. If you really want to you can buy new actual Volvo nuts but expect to pay $10 per wheel for them new ($2/piece 5/wheel). Junkyard or nonVolvo is a better bet costwise.