Sticking with the shiny theme from yesterday, I was looking out from the footbridge at Ayelsbury station and noticed the state of the roof of an DMU.
It's not dirty, or at least not in the way we tend to think in model terms. There are streaks from the exhausts. Great black splodges of muck, but only black and quite a pure version of the colour. There's not brown or even grey in there.
Elsewhere though, it's not only clean but thanks to the efforts of carriage washing plants, burnished to quite a high shine. It doesn't show up in the photo but the colour was nearer silver than the white I assume they are supposed to be. You can see the reflection of the canopy edge quite clearly. Away from the exhausts, the effect was even more pronounced.
I'm not sure this could be modelled, at least not without people telling you you got it wrong. In out minds, up top of a coach is muck, not shine.