Mapserver - RGB Composite - Keep Color with exception

Question

I am currently having the issue that I want to give my nodata-values a specific color and keep the rest of the Map in the given RGB-values.

This is my standard-Map:

I added the following statement to my mapfile in the layer-part:

    PROCESSING "SCALE_1=1,2000"
    PROCESSING "SCALE_2=1,2000"
    PROCESSING "SCALE_3=1,2000"
    PROCESSING "BANDS=3,2,1"
    METADATA
        wms_title "sentinel_2rgb"
        wms_srs "EPSG:25832"
        wms_extent "-1877994.66 3932281.56 836715.13 9440581.95" # https://epsg.io/25832 projected bounds
    END
    CLASS
        NAME "nodata"
        EXPRESSION ([red] >= 255 AND [green] >= 255 AND [blue] >= 255)
        STYLE
            COLOR '#9AFEFF' # Electric Blue
        END
    END

Now my map is completely empty. I wanted to change the color of the completely white areas/nodata (value is 65535) to match my specific color. But apparently as soon as I set a single value/color the rest will not be drawn?

Answer 1

So what I did is Adding OFFSITE 255 255 255 to the mapfile, at least the white pixels will get transparent now.