Blue mixed with orange

I used QuarkXPress's Multi-Ink function, which lets you mix a color by using percentages of spot colors, to test this. I first made a brown by mixing 35C/45M/72Y/15K. Then I made a blue by mixing 100C/80M/0Y/0K. I finally made a Multi-Ink color by mixing 50% brown with 50% blue. It came out dark gray.