@BlueberryPup
Dirt colour varies in different areas of the UK, some is a bit redder, but where I am, in the north west of England, the soil is dark. We're in a wet area and fairly rural, so it gets pretty muddy. The footpaths have huge puddles for much of the year, even now, in the middle of summer, it is always quite mucky.
I can imagine the red soil being a lot more difficult to shift once it gets on your dog, than the dark mud we have here, but to some extent it may also depend on the size and coat of dog. I suppose their habits play a part also, some dogs love to swim, others like to roll in the dirt. So I'm guessing that all these factors can determine the frequency that you would need to bathe them.
Despite being cream, my breed is fairly easy to keep clean. I think it helps that they're very tall, really it is only their legs that get dirty. They also walk around puddles rather than going through them, and that helps. Once it dries, any mud just drops off, then I give a quick brush. We also check them over for bits of vegetation, sticky bobs, burrs and grass seeds - yesterday she came back covered in goose grass bobbles on one side of her neck. The fur is very long there so they were a pain to pick out.
She has just had a very heavy moult, so all the puppy undercoat is gone. She'll be in full adult coat for the first time later on this year. That'll be interesting, because we can't quite predict whether her coloured body patches will be more or less visible.