Yup. It's a Mongoose.
It's a fairly nice electronic Spyder clone from late 2003.
It's the direct successor to the Black Dragun series of guns and was designed by the same guy who does the Dangerous Power guns today.
More info here: http://www.pbnation.com/showthread.php?t=869664
Diablo has its own dedicated on PBNation here: http://www.pbnation.com/forumdisplay.php?f=332
Pretty dead there nowadays, since all the guns have been out of production for years and the Invert brand essentially replaced the Diablo brand in KEE's lineup.
Also, are you sure someone painted it?
Some of them came from the factory in that dust red color.