By default, the Grayscale property is 0, so the layer is shown normal ( enabled ). You can use the Grayscale property to show the entire layer in gray scale ( disable state). Use the DefaultLayer(exDefLayerGrayscale) property to specify the default value for the Grayscale property,  before adding any layer.  The Brightness / Contrast properties can be used to change the percent of specified color to be applied on the layer. The Selectable property specifies whether the user can select the layer at runtime. For instance, you can simulate a disabled layer by changing the layer's Grayscale property on True, and setting the layer's Selectable property on False. 

The following screen shot shows the layer, with Grayscale property on False ( by default ):

The following screen shot shows the layer, with Grayscale property on True: