Bitmap Tracer Dialog Box - Initial Color Tolerance
Color tolerance is how great a color change is required before the tracer considers two areas to be a different color.
This setting is used for the first of multiple passes. It is similar to the broad brush strokes used to create the underlying colors on a conventional painting.
As a trace proceeds, the color tolerance is reduced from the initial value to the final value, so the initial value must be the larger.
For a trace using only a single pass this value is ignored - see Final Color Tolerance.