Congratulations, 31Kilo, on joining the 457 fraternity. You will enjoy and appreciate the quality of your pistol and how well it shoots.
According to the SCSW, the duo-tone 457 was produced in 1997 for Zanders Sports. I assume that was the only year of production, as other models listed in the SCSW are listed by a range of years if they were produced more than once.
The SCSW also says that the value of the duo-tone models is twice what the other models are, assumedly due to relative rarity. We don't see that playing out in the auction or sales world, though. Still, for the trade you made of a pistol you paid $300 for, you did very well on this. Good on you!