All-over color is usually the best option for grey coverage, for vibrant reds, coppers, deep chocolate, or auburn tones. There are different types of all-over color products. Tone-on-tone color is an excellent option for blending grey; adding richness or vibrancy, or going darker. New tone-on-tone products provide beautiful, durable results with incredible shine and a minimum of upkeep, as roots are less obvious or non-existent. When a lighter shade is desired, a permanent all-over color is necessary.
All-over color is usually done in a single step, but to go from dark brown to a very light solid blonde, such as a platinum blonde, your hair may need pre-lightening. This service is called a bleach and tone. A pastel color, such as platinum, is added in an extra step. Think of Paris Hilton or Marilyn Monroe. The downside of lightening hair with an all-over color is that the roots will be 1/2" after 4 weeks. It is important to discuss what will be involved in retouching your color with your stylist. When going lighter, a higlighting service can easily triple the time that is required between color touch-ups.
If you want to cover grey but also want a highlighted effect, you can do both at the same time. You won't need highlights each time you come in for a retouch, however. Typically, an all-over color with highlights is done every three months, with the roots retouched once or twice in between with an all-over color service.