I'm colour blind, and strangely when I start watching something in black and white, I don't know it's in black and white! - I only realise when someone else men

I'm colour blind, and strangely when I start watching something in black and white, I don't know it's in black and white! - I only realise when someone else mentions it, and even then it takes a while for me to see it. It's weird, like my brain is automatically filling in colours that aren't there.