When I was visiting the Las Vegas Boutique last week, I bought a dark brown Santoni strap and deployment clasp to try on my Vintage Ingenieur Laureus. To my tastes, the experiment was a success.





A bit unconventional, perhaps; but I think the dark brown antiqued strap goes very well with the midnight blue dial. It makes the watch slightly less dressy -- which suits my current suburban, casual lifestyle in retirement. After all, it's been at least two years since I've worn a tie.
Some may see it as sacrilegious to tamper with the original configuration, but (1) it's still an IWC strap and clasp; (2) I've retained the original blue strap so the watch can be restored to original configuration; and (3) I'll keep the black IWC strap I first had put on the watch in case I decide I need something more formal.