That sounds like one of the class of revolver (not a derringer, which would have been a single shot or two shot pistol) called by collectors a "suicide special" because supposedly they were so cheap they were only good for one shot and only a person contemplating suicide would buy one.
None of my sources show a "Red Top", but there were ones called "Red Cloud", several models named "Red Jacket", and a "Red Hot."
There is mild collector interest if the gun is in top condition, otherwise, it is of interest only as a curiosity with a nominal value ($50 or less). Those guns were made by the hundreds of thousands from the late 1860's to around 1900, by a number of companies who put all sorts of fanciful names on them except, interestingly, their own. They sold in that era for as little as $.75 or $1.00 when a Colt Single Action Army sold for $15.00.
Jim
