Try it from the client:
geonet.esri.com/thread/183682-arcgis-javascript-how-to-layers-custom-field-value-rendering
// Key section of above link
var renderer = new ClassBreaksRenderer(null, "STATISTICS");
renderer.addBreak(0, 10, new SimpleFillSymbol().setColor(new Color([56, 168, 0, 0.5])));
renderer.addBreak(11, 30, new SimpleFillSymbol().setColor(new Color([139, 209, 0, 0.5])));
renderer.addBreak(31, 50, new SimpleFillSymbol().setColor(new Color([255, 255, 0, 0.5])));
renderer.addBreak(51, 90, new SimpleFillSymbol().setColor(new Color([255, 128, 0, 0.5])));
renderer.addBreak(91, Infinity, new SimpleFillSymbol().setColor(new Color([255, 0, 0, 0.5])));
layer.setRenderer(renderer);
layer.redraw();