They are, because people having varying numbers of Rods and cones in their eyes, it causes people to see colours differently.
Also there is a theory that everyone sees, for example, the colour red differently eg Red=yellow, but because we’ve been taught that, that specific colour is red, no one knows if everyone is seeing the same colour as another person.
a magician asks you to pick a card - any card, in fact. you do. they ask you to put the card back in the pack - anywhere in the pack, in fact. you do. they walk away. ten years later, your wife gives birth to the six of clubs. “is this your card?” the midwife asks, in a familiar voice.