I tried out a stamp on foam board. Sadly it isn’t Dollar tree stuff. This the paper won’t come of style. Sadly I couldn’t find any black or grey card to test it on. By the looks of it, it does work well in the table 🤪.

There might be something in this… However I am not really sure what I would use them for. A few things I have learned from this is to make sure the paint goes on thick enough to leave a mark. I am using extra thick paint, I might see how a thinned down version works.
It looks better if there are no large splodges of colour. I tried colouring individual stones, but to be honest it doesn’t really work.
I painted a dark background and to be honest it looks much better.👍

I am pleased with the results so far.
Thanks DMScotty!
I blasted off another stamp which can be seen at the top of the photo below.

The advantages of the 10mm blue foam is that it is waterproof and can be washed under the tap. It is a bit sturdier too being twice the thickness of the foam board. It also has the advantage of not having to have the paper removed.
The advantage of the foam board is that I can get it locally, it is easier to put even pressure on too.
I will have to make a 3×3 tile and compare the two types.
I do particularly like the planks.