Can I use a 15 volume developer with Demi permanent ammonia free hair color to cover and blend greys as well as slightly lift the base color?

Yes, you can use a 15 volume developer with demi-permanent ammonia-free hair color to cover and blend greys while slightly lifting the base color. The 15 volume developer provides enough lift for subtle color changes and helps the dye penetrate the hair effectively. However, keep in mind that the results may vary based on your hair's porosity and current color. Always perform a strand test to ensure desired results.