ColorMapEntry entry = sf.createColorMapEntry();
entry.setQuantity(fromExpr);
entry.setColor(fromColorExpr);
entry.setOpacity(opacityExpr);
colorMap.addColorMapEntry(entry);
entry = sf.createColorMapEntry();
entry.setQuantity(toExpr);
entry.setOpacity(opacityExpr);
entry.setColor(toColorExpr);