Consult a Colorist: Discuss any hair color changes you're contemplating now.  Semi-permanent glazes are great gateway dyes that give a hint of tint.  Permanent single-process color easily covers grays.  Golden highlights photograph best, adding depth, texture and sparkle, says Kyle White, an N.Y.C. colorist who has worked with Mariah Carey.  Book all appointments at once: for highlights or semipermanent color, every eight to 12 weeks; for single-process color, every four to six weeks.