A boy in a yellow t-shirt and pink sweater talks on a cellphone while riding a horse through a crowd of people who are looking on.
A boy has a yellow t-shirt and pink sweater.
If he is wearing the yellow shirt and pink sweater then he has them.
"A boy in a yellow t-shirt and pink sweater" is a rewording of "a boy has a yellow t-shirt and pink sweater."
A boy in a yellow t-shirt and pink sweater is riding a horse.