The Texture Map combo box is located in the middle of the Main tab sheet. It offers a choice between "Colored" and various grayscale variations. It is set to "Colored" by default, but this produces unwanted effects when using, e.g. the Surface, Paint or Erode main effects. That is why it is in many cases necessary to set it to one of the grayscale options.
The Texture Map Options
Gray - Average
Gray - Intensity
The original texture
The average value of all three color channels is used.
Grayscale conversion favoring mostly Green and Red.
Gray - Luminance
Gray - Photo Optimized
Gray - Red Channel
Similar to Intensity, but a bit more emphasis on Green.
Grayscale conversion using Green and a bit of Red. Recommended for photo textures.
Grayscale conversion using only the red channel.
Gray - Green Channel
Gray - Blue Channel
Gray - Yellow
Grayscale conversion using only the green channel.
Grayscale conversion using only the blue channel.
Grayscale conversion using only the red and green channel.
Gray - Magenta
Gray - Cyan
Grayscale conversion using only the red and blue channel.
Grayscale conversion using only the green and blue channel.
Depending on the texture the Texture Map options are more or less different or the same. They usually only differ in small nuances. But for a few textures a different grayscale option will produce very distinct effects. Especially the Edge main effects will produce variations with every Texture Map option.