“Oriental” paintings “don’t look Arab”

In a [humanities] class, we were analyzing “oriental” paintings, and several students remarked that the people in the paintings didn’t “look Arab” because they had a lighter skin tone, lighter hair, or lighter eyes. My teacher did not correct them and explain that Arabs come in all shades and sizes. This made me uncomfortable because I myself have been told I don’t “look Arab”. What is an Arab supposed to look like according to them?