STYLETHREAD -- LET'S TALK SHOP!

Has anyone tried L'Oreal Couleur Experte hair color?   It has intrigued me for awhile because it comes with color and highlighting cream.  The way it works is that you color you hair with the color and then highlight it with the highlighting creme in the kit.  The thing I am not sure about it how to handle touchups with the product.  L'oreal's website says that when it comes time to touch up, to leave the color on the roots for 20 minutes and then pull it through the rest of the hair for 5 minutes.  However, if I pull it though the rest of my hair, won't that cover up my highlights from the previous time?  Won't I then have to rehighlight my entire head?  I don't think you are supposed to do that because highlights on top of old highlights can cause hair breakage.  However, if I don't pull it through the rest of my hair, the color from the previous time won't be refreshed.  I will still have the old highlights from the time before, but the color will have still faded.  Their instructions do not cover how to handle the highlight retouch up.   I am a little confused   I am probably overanalyzing this due to the mathematician in me, but can someone tell you if you have had any experience with touchups using this product?