Hey,
I'm not on this site often, but I'll note that mine were gray/grey as well. But y car was originally, or spent the first few years of it's life in Europe (67 122s).

I was not especially happy with cardboard in my car and I like to improve (?) items when appropriate. But I am odd, too odd for many. I made one of these panels (one so far-passenger side) out of 1/8th inch mahogany plywood- and stained them (it) black. I also wrapped IPD door guard trim around the cut edge for a finish. I wanted to add sound deadening material, but there's really no more room.

It sounds impossible, maybe stupid- but that's a value judgement. It's not real easy making these and most of you have better things to do than spend your time on such projects. But everyone is different.

Second, that factory cardboard bends in two different directions for a proper fit. All of my cabinet maker friends insisted that I was not going to be able to make a compound curve from plywood. "It's impossible". I love such affirmations... I did. But that is the time consumer. The panel on the passenger side was a VERY tight fit, and the map tray, etc. is back in place (less the bracket) I may not need the map tray bracket as the fit is VERY tight. But I am going to revisit that in installation in the spring.

So I have black stained mahogany, not cardboard, kick panels. It was my choice. I thought I would share that, just in case you want to be as adventurous.