Large pots demand a heavy coarse clay in order to withstand the stresses created when they are fired. One of the advantages this gives, is that when you sand blast away the fine material on the surface of the pot, you reveal all the coarser sand, aggregate and other bits that lie beneath. The effect is one similar to natural stone, and that is what has been done to this pot.
The change in colour and surface finish suite some designs of pot better than others, but this one seems to like it a lot, and whether you plant a large shrub or tree in it, it is going to give you lots of pleasure in your garden.
That same mixture of heavy strong clays and the fact that it has been fired at 1000-1200 degrees centigrade also mean that the pot is frost proof, and that you can leave it outside in all but the most severe of British winters.
Just to be on the safe side though, remember to use a good amount of drainage material in the bottom of the pot, and then a free draining compost to fill it up. This will aid the drainage giving extra protection, and providing a good growing environment for the plant.
Putting the pot up on 3 pot feet will also help the drainage as well as giving the whole combination a bit of extra height so it stands out even more.