I had a MRI of the left knee. My doctor thinks I tore my meniscus. On an MRI what color would you look for black or white for a tear?

Depends. The answer depends on the specific technique used in any specific sequence. For example, in T2 weighted images, the tear is seen as a white line extending from inside the meniscus to an outside articular surface. In T1 weighted images, a meniscal tear is a relatively dark line. And in other sequences, the tear can be relatively lighter or darker than surrounding tissues. Discuss with your Doctor.
Depends on the image. Tears of menisci can show up on MRI as distinct areas of seperation ordefects are usually seen as defects in the dark background may evevn appear grayish if the tears are not complete.