Grey stones? Maybe not.
The older classes might be inspired by junior infants day on the beach.When you begin to collect stones it is amazing all the different colours and textures you will find.
Wicklow library have some interesting books on stones.It’s interesting to work out the colours in stones by making paintings of them.When you paint you really have to figure out exactly what colours, patterns and textures are in the stone.
Here is a good website on sea stones