When you say "they" who are you referencing? If you bought from a dealership chances are you got the bin oil they buy in bulk. A typical dealership will only carry one weight which is 10/40 which can also be used in sport bikes. It's unlikely for a shop to stock two weights in bulk. The 1900cc vtwin and wet clutch design demands the heavier weighted 20/50. If bought from a private owner, unless you have receipts and a good log, who's to say what they actually used. Either way, the 60-70 dollar oil change should be included as you run through all the fluids on any used vehicle purchase. I'd also plan to swap out the transfer case oil too. Be sure to use a gear oil specifically listed for GL-4 applications too, the ratings of GL-5 are not successive which means they are application specific, not that a GL-5 covers GL-4 applications. This way you know when the clock starts and stops on each of the fluids.
Also remember that a dark color is not an indicator, in fact, it does appear typical and that's actually a good thing b/c it's working. Darker color just means the oil is doing it's job cleaning internals, with the liner's wet clutch design and heat generated, it is extremely harsh on oil. It's no accident that the bike comes with an oil cooler as this is needed to keep things cool. For a quick check wipe your index finger in the oil and give it the two finger check by clinching, then separate your thumb. If the oil clings (or stands up) as you separate your two fingers chances are viscosity is fine. I know it's not very scientific, but does give piece of mind.