This could be a yeast problem. I have a westie mix that had this problem when we adopted her almost a year ago. It affected her eyes, muzzle area, feet, and tummy (she had black skin there).
What are you feeding your dog? A grain free diet helped Maddie immensely, as did changing her food bowl to ceramic, rather than stainless steel. Her water bowl is glass. It took awhile, b/c you can't bleach out the staining; it has to grow out/trimmed off over time.
Here's a link to a kibble review site. I'd switch to a food that rates 5 stars; 4 at the least (and preferably grainfree). If you switch, do it slowly, so as to avoid tummy upset. Also remember that you can feed less of a grain free kibble b/c it's more nutrient dense (in fact, if you overfeed it, it can cause tummy problems).
Something that helps my westiemix with her itchy paws (she also has environmental allergies) is to soak her feet in a Betadine/water mixture every day (you can also wipe it on other affected areas). It's antibacterial and antifungal. Here's a link with more information: Irritated Pet Paws | How to Relieve Your Pet?s Irritated Paws
Beth, mom to adopted rescues: Maddie (malti-poo/westie, age ~6), and Jackson (boxer, age ~8), and various fosters from time-to-time
RIP Sunny (toy poodle) - traveled to the Bridge June 2015