Title:Red shirt, blue shirt.
Disclaimer: Not mine, more's the pity.
Ianto thought Jack didn't know him. But Jack did. Jack knew for example, red shirt days meant vulnerability, hurt, loss, those days, Jack hurt to. Blue shirt meant strength, determination, a good day, a day Ianto felt he could go on, so could Jack. No shirt? Those were positively the best days, Ianto was free, uninhibited, those were the days Jack lived for, those were the days when Ianto was his alone.
He never gave comment, but he knew what flat, spiky, or odd tin tin hair meant. He knew about the creases on Iantos pants, his sock choices, yes, Jack knew Ianto very well indeed.