For a contour map, the only time you should set the colormap to use logarithmic scaling is when the Level method for the contours layer is set to Logarithmic. If you use the Simple contour level method, and a logarithmically scaled colormap, then most of the colors will be squished at one end of the color scale.
Select the contour map, click the Levels tab in the Properties window, and change the Level method to Logarithmic. Setting the Level method to Logarithmic first automatically checks the Logarithmic scaling option in the Colormap Editor.
Updated October 25, 2018