Engine has rough acceleration and the coolant is dark.

Hello,

It is likely that the coolant needs to be flushed. Coolant gets dark overtime with contamination, it should not be dark you should be able to tell the color of the coolant (green, pink etc.).
Here is a helpful guide on how to flush and fill the cooling system:

https://www.2carpros.com/articles/coolant-flush-and-refill-all-cars

As for the rough acceleration, it could be due to a number of reasons. It could be due to having a weak fuel pump, dirty fuel filter, clogged air filter, worn out spark plugs, vacuum leak, dirty mass air flow sensor etc.

Is the check engine light illuminated? Many times, with drivability issue the engine light gets triggered. If so scanning and retrieving the code(s) can help with the diagnostics.

https://youtu.be/vMwTzURWXmk

The best course of action would be to take a look at each item and take necessary action. It might be a good idea to do an engine tune up.

https://www.2carpros.com/articles/how-to-tune-up-a-car-engine

I have attached diagrams for your reference.

Please let me know if you have any questions.
Thank you.