List params = new ArrayList();
params.add(0, expr2); //expression
params.add(1, ff.literal(2)); //classes
function.setParameters(params);
Object object = function.evaluate(fc);
assertTrue(object instanceof RangedClassifier);
RangedClassifier classifier = (RangedClassifier) object;
Color[] colors = brewer.getPalette(paletteName).getColors(2);