I agree with Pat - that looks normal to me, even the brown 'spot', which is just some unique coloration on her coat. Kipawa is also lightly pink around his lower tummy/penis area. There is just a little less fur there, and so I think the pink skin is just more noticeable.
I have also noticed that My B will have an extra pink belly after he's been sleeping all rolled in a little ball. I assume it's just the warmth and blood flow that makes his belly look especially pink. When he's cold, it's paler. And worries aside, there is nothing sweeter than a pink, sweet B belly!!
I agree with Bewler. When they get warm their bellies get pinker. More blood flow to the outside to dissipate heat. I was unaware however that they would possibly have coat coloring on their bellies. Both of my B's have white bellies with dark skin spots. The things you learn on the Basenji Forums!