General White guinea pig tummy

I've noticed my white guinea pigs tummy fur is turning yellow. Is this common for white piggies? I spot clean the cage daily and do an entire cage cleaning once a week. Is there a way to help absorb the pee better? Or should I do a wipe down with pet friendly wipes on my piggies tummy? I really dont want to give him a bath since I've heard it's only good to do it once or twice a year and i gave them both a bath once i got them. He isn't in pain or showing any signs of discomfort. My worry mainly is that the pee dries and clumps on his fur and I really dont want that.

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