What Causes Light Brownish Discoloration On Abdomen?

I have some area of light brownish discoloration on my abdomen.Sometimes it takes on a light redish/purpish hue. This is more like spots rather than striae. I have had 4 children, including twins, but have doubts that these spots are related to my abdomen 'stretching'...just doesn't look like 'stretch marks' I am being treated for hypertension, hyper-cholesterol, and I am currently still about 35 lbs over-weight. I doubt cushings syndrome.