To format the colors of the levels in a surface chart, you must format the legend key (legend keys: Symbols in legends that show the patterns and colors assigned to the data series (or categories) in a chart. Legend keys appear to the left of legend entries. Formatting a legend key also formats the data marker that's associated with it.).
Note When you click one of the Placement options, the legend moves, and the plot area (plot area: In a 2-D chart, the area bounded by the axes, including all data series. In a 3-D chart, the area bounded by the axes, including the data series, category names, tick-mark labels, and axis titles.) automatically adjusts to accommodate it. If you move and size the legend by using the mouse, the plot area does not automatically adjust. When you use the Placement options, the legend loses any custom sizing you may have already applied by using the mouse.
Note You can delete the legend when you're done changing colors, and the colors you specified will remain in the surface chart.