Solid Hardwood, Engineered and Laminate Flooring - Master bedroom with 2 different wood floors

We're repairing the home and removed the carpeting from the master bedroom. We wanted to sand and put a new finish to the hardwood floors. But we found that the original homeowners had replaced half of the wood floor. The floor isn't leveled and the wood grain differs from each other. Half of the floor has a nice finish with a very bright solid oak color. The other half doesn't have a finish and has a dull dirty light brown color. What are our options?

have you tried using a small hand held sander on the "dirty light brown color" to see if it cleans up? Do the same on the "nice floor" and compare what they look like in their natural state.

One other thing to consider is furniture placement in the room, will the bed/dresser/amoire/area rugs be over the 'dirty' section leaving the nice floor exposed?