Even allowing for a mucky drizzly day the horse is looking quite grey and due for whitening.
They literally paint some of it, chalk chippings have also been used.
The underlying rock is fairly bright limestone but it soon turns grey on being exposed to the weather.
When close to the figure like this, it seems rather smaller than you might have expected - considering it is strikingly visible when driving or on the train heading north from many miles away.
It has even been spotted in exceptional conditions from mountain tops in North Wales. Link