After seeing Amy in that striped shirt at the retreat, I thought it looked slightly too familiar. So I've just spent the last hour googling and trying to match it to Dan's ties. (There's one scene in 4.02 where he's in DOUBLE stripes – both shirt and tie. It's not a match, I just loved the double stripes.) I think I've gone over to the bad place and it's entirely your fault. I don't regret it though 🙂
If it helps, I swear I remember Dan having a striped tie sometime in season 1 (I think it’s cream and red – his colours are a lot lighter in season one though, lots of light gray suits) I just can’t be bothered to track down which episode it’s in (because even I have limits).
More to the point, if you all get to good at this, I’m going to be completely stuck when the new season airs – you’ll probably come up with much smarter things than I will!