I thought the pants I'm wearing today were purple... until I saw them laying on my bed next to my socks while I was getting dressed this morning. My socks I would describe as blue.
Seeing them next to each other though... they were pretty much the same colour.
So why would I look at one and think "purple" and then look at the other and think "blue" when in fact when you compare them directly, they're the same.
The pants colour question got more interesting just now. Someone said to me "Is your skin really that white?" I touched my back and realised my huge pants had ridden up above the level of my trousers. Being so huge they managed to ride up that far and not even give me a hint of a wedgie. As a frame of reference, they're a bit like my Dad's trouser's now he's reached that age where his elasticated waist band doubles up as a training bra.
"Oh, no, it's my pants."
"Good, because no-one wants skin that colour."
She thought my pants were white. Or she could think I was so ill that my skin had gone beyond white into blue.
I'm tempted to photograph my pants and put them on the internet to let others make up their own mind.