short getDefaultColix() {
		if (defaultColix != 0)
			return defaultColix;
		int argb;
		if (cutoff >= 0) {
			indexColorPositive = (indexColorPositive % JmolConstants.argbsIsosurfacePositive.length);
			argb = JmolConstants.argbsIsosurfacePositive[indexColorPositive++];
		}
		else {
			indexColorNegative = (indexColorNegative % JmolConstants.argbsIsosurfaceNegative.length);
			argb = JmolConstants.argbsIsosurfaceNegative[indexColorNegative++];
		}
		return Graphics3D.getColix(argb);
	}