Permanent dyes open up the hair shaft by using chemicals, striping color away so it can add new color in. This explains why it is difficult to drastically change colors. Typically, the old color of your hair is being mixed in with the new color. To avoid this, the process can be broken down into two steps, color removal and color addition.
Permanent dyes are more natural looking than semi-permanents .
Honestly, we can't tell the difference between Miss Clairol and Miss Clairol Ultress, except the packaging. Miss Clairol's colors tend to be wimpy and it still damages your hair significantly. It is rather consistant and predictable. Ultress- 9 Excellent product if you want to go blonde. Other colors turn out great too.