The main reasons I bought it despite the color were it had all the features/options I wanted, the mileage was low and it appeared to be in pristine condition. There weren't too many nice K75Ss for sale around that time, either.
I also thought that the yellow might be a bit brighter in person than in the photos I had seen on IBMWR. Flew from Hawaii to Georgia to make the buy and ride back to the West Coast for shipment.
That all went well and when we uncrated the bike near the port in Hawaii my wife immediately changed it's name to "Chiquita" and I agreed that that was a tad better than riding around on a Dafodil.
I also agree with your comment about yellow for a bike; a much brighter shade such as seen on Porsches or my Nolan helmet would have been great; but alas, those in the design department at BMW chose that yucky pastel instead. Perhaps it has some significance in Senegal but I don't know, never been to Dakar or any other part of that country so I can't say.
I used to have a Mercedes 280SE 4.5 that was silver, an Alfa Romeo Spyder that was silver and when I bought my '85 K100RS off the showroom floor I almost bought the silver one parked next to the Red Metallic one that I finally decided on. I think silver and grey are very cool, especially on Teutonic machines such as ours. (but that Rot Metallik was hot!)
While it took me a while to actually strip the tank down to bare aluminum and polish it out, get the rest of the bike painted in Mercede's Tenoritgrau (steel gray) at least the only scrambled egg color around my house was on my breakfast plate thereafter.
Here's the before and after shots so it can be seen how much I wanted to change the color:
(but before I go let me also add that I'm a strong believer in "To each his own" and I don't mean to step on Slipster's or anyone elses toes here. But Dakar Yellow or anything close is simply not my cup of tea.)
and now BERLINA