My dog has a weird brown spot on her side. what could it be?

My dog has a brown spot on her side. Her fur is white on top of the brown spot on her skin. It is approximately 2-3 inches in diameter. We shaved her fur to look at it better and it just looks like a discoloration or possibly a bruise. When we got her the old owners said she had gotten nipped by another puppy but we've had her for a little over 3 weeks now and it hasn't gone away. She is nearly 5 months old. She does have brown on her ears but the rest of her is white. Is this just a new spot of color on her or is there something wrong?