I have two articles I can share with you, with regard to protein:
From Paula Begoun:
Proteins are long chain molecules that cannot be absorbed into the hair shaft.
Proteins are often partially hydrolyzed to help them cling better to hair. The best thing that proteins can do is coat the outside of the hair, filling in gaps between cuticles, which can protect the hair and add a soft feeling.
Adding protein to hair care products does not restructure or add to the hair’s composition.
As conditioning agents, keratin and amino acids cling poorly to the hair, so they get washed down the drain.
You can’t get protein from hair keratin. Other forms of keratin that comes from plants can be good conditioning agents, but they can’t repair hair.
From Mut, a few years back:
Description: Insures marvelous color results by equalizing hair porosity. Repairs protein bonds and protects against chemical damage. Seals color, adds body, volume and sheen.
Directions: Apply to towel damp hair. Apply colour after 20 minutes. Do not rinse.
Ingredients: hydrolyzed keratin protein, hydrolyzed wheat protein, keratin amino acids.
You may find that your hair has reached a point that it just won't hold color anymore. It is likely that you have damaged your hair shaft so that the color molecules just wash away rather than getting trapped inside.
Head down to your local beauty supply store and pick up something called protein filler. They sell protein fillers in various shades but I always choose the neutral protein filler, which is clear. A large sized bottle of neutral protein filler costs around $5.00 and will make all the difference in the world with how your dye job comes out.
Get a box of hair dye and have everything ready like you are going to dye your hair. Start by getting your hair damp and then saturate it with the protein filler. Once you have the protein filler on your hair you will need to let it set for 20 minutes.
After 20 minutes you are ready to dye your hair. DO NOT rinse the protein filler out of your hair before dying it. Just apply the hair dye like normal right over the top of the protein filler and follow the timing instructions on the box of hair dye for how long to leave it in. When the time is up rinse your hair thoroughly and condition it using the conditioner that came with your hair dye.
Protein filler works to help seal the color into your hair shaft so it will last longer. Not only that, but it helps the color go on more evenly so you don't have spots that are darker or lighter and it helps to repair the damage to your hair at the same time.
While your hair dye may not last as long as if you had applied it to virgin hair, it will last much longer than it would without using the protein filler. Apply any leftover protein filler to your hair periodically to help condition your hair and keep it in great shape.
"I'd like to see my colourist again in 1-2 weeks for a re-dye. If I want to use a protein filler from Sally's beforehand, should I do it the day of the appointment?"
Now that you know a bit more about protein fillers, purchase some and take it to your stylist. Have her apply it before she dyes your hair. Then you can see for yourself if you think they are worthwhile.
Let us know - I haven't tried any yet but have been considering.