Re: Colt No. 3 Derringer
Your photos are a little better than those posted last year but the side views are still fuzzy. For detail, a camera with macro setting used in natural light is best.
Flayderman's Guide states approx. 48,000 made ca. 1870-1912, which may date yours 1890s, and lists value range from $275 for Good condition to $650 for Fine condition. If the nickel plating is original (appears to be in top view) it should fall at top of that range, and the ivory grips will add a premium (assuming both are intact).