Simple transparency / opacity is achieved by only specifying the OPACITY parameter (this achieves the same effect as the legacy LAYER OPACITY parameter):
currently opacity is set in openlayers API, but for google kmz layer need to specify opacity in mapserver to generate correct bitmaps with alpha channel
since mapserver 7.0 opacity option is in composite section of layer, and does not work inside layer https://mapserver.org/mapfile/composite.html#composite
Simple transparency / opacity is achieved by only specifying the OPACITY parameter (this achieves the same effect as the legacy LAYER OPACITY parameter):
currently opacity is set in openlayers API, but for google kmz layer need to specify opacity in mapserver to generate correct bitmaps with alpha channel