Here is the million-dollar question:-) But already… is it possible? The good news is that yes! To help you do this, you can count on your best ally : lime water. Lime water is the water used to extinguish quicklime. It is therefore still lime-laden but no longer has the white color that inevitably fades the dye. Its transparency makes possible to create very bright tones without blocking the support.
You can apply it in fresco (fresh in fresh), patina or fixative. More information here.