Anyone knows how I can configure the godiva viewer in order to get a specific colour palette and specific range of values?
This is an example, where the colour palette is the default, but the range of values is updated according to the file displayed.
The wiki only shows how to add new palettes.
In Godiva2, you can click on the colorbar and select a different colormap from the list of options provided by the WMS server, and also select the number of colors desired.
The default query looks like this:
http://thredds.met.no/thredds/wms/eumetgrid/met.no/eobs-gridded-data/eobs-gridded-data_0.25deg-reg-v3.0-2009-10-12.nc?LAYERS=tg&ELEVATION=0&TIME=2009-10-12T00:00:00.000Z&TRANSPARENT=true&STYLES=boxfill/rainbow&CRS=EPSG:4326&COLORSCALERANGE=-50.0,50.0&NUMCOLORBANDS=20&LOGSCALE=false&SERVICE=WMS&VERSION=1.3.0&REQUEST=GetMap&EXCEPTIONS=XML&FORMAT=image/png&BBOX=-6.375,25.75,51.5,83.625&WIDTH=256&HEIGHT=256
producing: 
but increasing the number of colors from 20 to 64, using the "redblue" colormap, and changing the colorrange from -10 to 30 looks like this:
http://thredds.met.no/thredds/wms/eumetgrid/met.no/eobs-gridded-data/eobs-gridded-data_0.25deg-reg-v3.0-2009-10-12.nc?LAYERS=tg&ELEVATION=0&TIME=2009-10-12T00%3A00%3A00.000Z&TRANSPARENT=true&STYLES=boxfill%2Fredblue&CRS=EPSG%3A4326&COLORSCALERANGE=-10%2C30&NUMCOLORBANDS=50&LOGSCALE=false&SERVICE=WMS&VERSION=1.3.0&REQUEST=GetMap&EXCEPTIONS=XML&FORMAT=image%2Fpng&BBOX=-6.375,25.75,51.5,83.625&WIDTH=256&HEIGHT=256
producing:
If you are not happy with the available colormap options, you would need to contact the provider of the WMS service, and ask them to add your favorite colormap as an option.
I'm not sure I'm understanding your question, but the color palettes and the default range for different variables are configured on the ncWMS side, not on the godiva2 side. Perhaps you can explain a bit more about exactly what you are trying to do?