What color do green and purple make?
Green and Purple make grey.

Green and Purple make grey, #414f58. That is the result in equal parts, mixing pigment rather than light - paint, ink and dye all behave this way.
Equal parts green and purple · #414f58
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 green, 1 part purple · #207a45
Equal parts · #414f58
1 part green, 3 parts purple · #60266b
Lighter and darker
With white added - a tint · #a0a7ac
With black added - a shade · #272f35
Why it works
Pigment mixes subtractively: green paint absorbs the wavelengths it is not reflecting, purple absorbs its own set, and grey is what neither of them absorbed. This is why paint behaves differently from a screen, where light adds together instead.
Frequently asked questions
What color do green and purple make?
Green and Purple make grey, #414f58. 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 sage. 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 green than purple?
Three parts green to one part purple gives teal. Reversing it to one part green and three parts purple gives indigo 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.