Create a layer based on RGBA netcdf data

A special case in the NetCDF files are goegraphical grids which do not contain values of a parameter, but contains the RGBA value of the colour that should be presented at that grid point. This kind of information is usually found in satellite products, where the values of different bands are combined (composited) into one RGB or RGBA value. The value of the parameter at a grid point is the value that should be plotted on the visualisation. You could see these fields as color photos, where each pixel is georeferenced.
The CF-conventions currently have no way to describe these parameters, so these files are generated as fields of 32 bit unsigned integers, each containing an RGBA value. The configuration of the layer tells the service that the parameter values should be interpeted as pixel color values. The service can then reproject the image from the source projection, if needed, by doing a nearest neighbor "interpolation".