Hair color, fading and porosity

Hi!
I double-process my own hair and have had considerable trouble with fading color. I also switched brands of bleach and my last couple of touch-ups have resulted in a slightly different color near the roots for about an inch than the rest of my hair. I believe the problem is a difference in porosity. I have seen protein fillers that report to correct uneven porosity and help the hair hold the color longer and more evenly. Has anyone used these products? What did you think? There are two methods of application listed on the bottle: one says to use the product before processing and the other says to add the product to the color during processing. Does anyone know how these application methods differ in the outcome? Besides neutral there are a few colors - what are the colors for (the platinum color has me a little baffled)? What do others do to resist fading and to even out hair porosity?
*By the way, if you`re from Chicago check out my post under Personals.
Thanks.