I did noticed same color on the window frames in some Märklin models.
An exemple are 37069 EP 3/6 K.Bay.Sts.B. and the new württemberg wagons.
When i did visit hobbystore before christmas day,i saw the new wagons and the window frames are painted with the lemon color!
Same color in the EP 3/6 window frames...
In fact did correct color on the prototype frames was wood treated with varnish.
Märklin do some problem with the color scheme of their models.