Permanent Blue Hair Dye
A: At present, I don't know of any blue hair dye that is permanent. Even the Goldwell Elumen hair color you mentioned above isn't permanent, although it is long-lasting. There are some new products available by various fashion hair color manufacturers that upgrade their existing color formulas to last longer.
1) When shampooing your color-treated hair, always wash and rinse the hair with cool water. This helps to keep the cuticle layer closed and will help the color to last longer.
2) Use a clear-coat color glaze. After applying your semi- or demi-permanent hair color, use a clear-coat glaze process (available from many manufacturers, and applied just like demi-permanent color) which will help to seal the hair, hold in the color, and give the hair a brilliant shine.
3) There are additive products available at your beauty supply store that will help to prolong the life of semi- and demi-permanent color. Mix these with your favorite color product to prolong the life of your color.
4) Pre-soften or pre-lighten the hair. If your natural color isn't already light blonde, you will want to pre-lighten the hair before using a fashion color. These bright colors work best on light hair, and the lighter the hair the better the result. In addition, the lightening process opens the cuticle layer and allows for deeper penetration of the color.
Skip any conditioning between the lightening and coloring steps for maximum penetration. Use an acid-balancing conditioner after coloring to seal the cuticle. If your natural color is already a pale blonde, you may still need to pre-soften the hair. Use a cream-based color developer alone on the hair for 10-15 minutes, rinse and then apply the color as normal.
These tips won't provide permanent coloring results, but they will help your semi-permanent and demi-permanent color to last longer.
©Hairfinder.com
See also:
Shampoo and conditioner that doesn't make hair color fade fast
How to make your hair color last longer
Things that can go wrong when coloring hair
Can I do blue highlights with foil on blue black hair without bleaching it first?
Would my brown hair have to be bleached before dying it blue?