arcgis desktop - Mapping continuous vector data on a continuous colour gradient in ArcMAP 10

I'm plotting vector data for different attributes for countries across Europe. I've used symbology to plot categories of countries. However, the data are numbers so are on a continuous scale. I would therefore like to plot the numbers in each country on a continuous colour or shading gradient (the default for raster data), where the number is each country is represented as a point on the scale rather than interval scales. This will make the data much easier to interpret. I cannot find a way to do this in ArcMap 10.

Does anyone know a way that this can be done?