What color do yellow and purple make?
Yellow and Purple make brown.

Yellow and Purple make brown, #593314. That is the result in equal parts, mixing pigment rather than light - paint, ink and dye all behave this way.
Equal parts yellow and purple · #593314
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 yellow, 1 part purple · #b4b90e
Equal parts · #593314
1 part yellow, 3 parts purple · #73115c
Lighter and darker
With white added - a tint · #ac998a
With black added - a shade · #351f0c
Why it works
Yellow and Purple sit opposite each other on the colour wheel, which makes them complementary. Complementary pigments cancel each other's reflected light, and what survives is a muted brown. Every complementary pair does this - it is the standard way to mix brown without a brown tube.
Frequently asked questions
What color do yellow and purple make?
Yellow and Purple make brown, #593314. 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 yellow than purple?
Three parts yellow to one part purple gives lime. Reversing it to one part yellow and three parts purple gives purple 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.