Preheat the oven to 500 degrees F.
In a small bowl, combine the black pepper, the green pepper, the white pepper, and the salt. Rub the meat with the pepper-salt mixture. Sear meat in hot skillet until browned all over. If tenderloin is too large for skillet, cut meat in half. In an oiled roasting pan roast the fillet in the middle of the oven for 20 to 25 minutes, or until a meat thermometer registers 130 degrees F for medium-rare meat, and let it cool to room temperature.
The fillet may be roasted 2 days in advance and kept wrapped and chilled. Slice the fillet crosswise, arrange it on a cutting board or platter, and garnish it with the parsley. Serve the beef with the Sour Cream Horseradish.
Combine all ingredients. Chill.