your mention of brown sounds normal. The white speckles and white electrode could mean the plug is too hot. Make sure the plug you are using is the correct heat range. Other causes could be overadvanced ignition timing, lean air/fuel mixture, vacuum leak (intake manifold), sticky valves or insufficient cooling.

Is the engine efi or carb? Have you changed anything lately such as the intake or carb? Are the correct spark plugs being used? Have you messed with the timing? Anything out of the ordinary happening? later