By default, Solve works in Preview mode. The variation is computed, but is not actually created. Instead, an outline of the variation is superimposed over the current part. This gives you a good idea of what the new variation will look like without creating any new geometry or overwriting any existing geometry. If the preview indicates that the new variation is acceptable, you can actually create the new variation by re-solving with the Keep or No Keep options. The preview lines are drawn in the current PD_PREVIEW_COLOR color (MAGENTA by default). Preview lines are removed from the viewport by the next Solve command or when you click End.