Range Hood venting
You could build a soffit, framed and drywalled or out of material that matches your cabinets. Or just make the duct out of (or wrap it with) copper or stainless steel. One other possibility would be to hide the duct behind a wrought iron or stainless steel pot rack.
It would be easier to make suggestions if we could see a picture of the area.
"The physician can bury his mistakes, but the architect can only advise his clients to plant vines." -- Frank Lloyd Wright