I would agree–starting with a darker base color will make a big difference. It looks gray because in the sketch the majority of it is gray, which makes the black area look like it’s just a shadow on a gray part.
With black metal you would see more of the black color showing through on the body itself, not just in the shadow. You can use highlights right along edges and corners to bring out the shape. A matte finish may mean the highlights are not 100% white or that they’re more diffuse vs. a hard line, but you can still use them to create contrast without making it look reflective. Don’t be afraid to put a highlight right next to a dark section–contrast makes things pop. Your bigger highlights might be more of a subtle gradient on flat surfaces, but you can always put a thin white pencil line along an edge to punch up the shape.
This gizmo isn’t matte finish, but you can see how the black shows through alongside sharp white highlights. To make it look matte you can reduce the number of “color bands,” make the transitions between colors less hard, and/or use gray instead of white to highlight. Poke around an image search for black kitchen appliances and study how the highlights look.