Since it's the company's fault, I would rip the concret out and have them re-do it if you are not happy.

Have them acid wash the whole thing so it all blends.

There are multiple products available to color concrete that will fix your problem and are a lot cheaper and less intrusive than demolish and replace. Most concrete products have bean around long enough to know they hold up well and will give you a nice finish for a long time. We have used these products with good success. Call around in your area for a concrete contractor that specializes in concrete refurbishing then get the concrete plant to pay for the repairs or do not pay the existing concrete bill.