Forage caps typically followed the main colour of the uniform.
I copied this image from the Internet, so can’t speak for the provenance, but the top right is pretty typical from what I’ve seen for forage caps for other Napoleonic soldiers. I’ve seen Wurttembergers throughout Faber du Faur’s prints wearing blue forgae hats with red or yellow edging depending on the uniform facing. Admittedly not Bavarian troops, but the Portuguese Legion are also shown with brown caps edged with white that again matches their uniform and facing colours.
Hope that helps!
