i changed my brake fluid and bleed them maybe a little extra to get the old fluid out about 3 months ago, and driven the car i would say about 10 times give or take within that limit just normal driving most of the time but do get on the car, but what would make it darken in color so quickly , using Motul rbs 600

 

If the seals have already been deteriorated by the old fluid then it stands to reason that you would still get some discoloration of the new fluid due to the seals being attacked by the old fluid.
If you are totally "****" about the fluid color then you would be looking at rebuilding the whole brake system with new seals...Oh yay..oh Joy..oh money...!
BUT if the system is working and you can live with a little "off color fluid" then I personally would just say "fugg it"!
Another thing pops into mind is the type of fluid though..and I would get opinions on what the best fluid is that you can run..(that is both compatable to the system and works well with it.)