Sharpie will show in a blueish tone in a black seatpost. In my experience this method will still create a small difference each time you adjust the saddle but on the plus side it will also allow you to compensate for different shoes soles or other factors that can affect saddle height
Cheers all.
Rubberducky, it’s not that I can’t get it high enough, more that’s I am too often finding myself not quite right on it, even when I tried the insert.
Recycled, that sounds like my kind of technology.
M_V, black seat post but perhaps there is a suitably tough and thin white marker that would work.