What is colour blindness and how does it affect people?
Colour blindness, which is also known as colour vision deficiency (CVD), is a condition where people see colours differently to the majority of people.
It affects approximately one in 12 boys and one in 200 girls worldwide. In the UK, about 4.5 percent of the population, which means about three million people, are colour blind.
Marcus is colour blind and he's unable to tell the difference between colours like purple and blue, and orange and green.
He was first diagnosed with the condition at the age of six.
Marcus spoke to Newsround about living with colour blindness and how it affects different areas of his life including school and playing sports.