What color do orange and black make?
Orange and Black make brown.

Orange and Black make brown, #663300. That is the result in equal parts, mixing pigment rather than light - paint, ink and dye all behave this way.
Equal parts orange and black · #663300
Change the ratio
Very little of a mix is ever half and half. Shifting the balance moves the result along the range between the two colours.
3 parts orange, 1 part black · #b35a00
Equal parts · #663300
1 part orange, 3 parts black · #261300
Lighter and darker
With white added - a tint · #99734d
With black added - a shade · #331a00
Why it works
Adding black to orange makes a shade. Black absorbs across the whole spectrum, so the result keeps its hue but loses brightness and some saturation, which is how orange becomes brown.
Frequently asked questions
What color do orange and black make?
Orange and Black make brown, #663300. Mixed in equal parts that is the result you get with paint, ink or any other pigment.
How do I make the result lighter or darker?
Add white for a tint - here that gives grey. Add black for a shade, which gives black. Add white a little at a time, because it takes far less than people expect to shift a mix.
What happens if I use more orange than black?
Three parts orange to one part black gives rust. Reversing it to one part orange and three parts black gives black instead.
Does this work the same way on a screen?
No. Screens mix light additively, so red and green light make yellow there. These results are subtractive - paint, ink, dye and pigment - which is what people mean when they ask what two colours make.