I setted the Colors attribute in the filtered navigation. If a search a product, all the colors are shown but when I click on a single color, for example "blue", the "blue" products aren't shown and are shown all the configurable product that have an associated product in blue colore. To explain well, I attach some screenshots.
Those 4 backpacks are displaying when you filter by "blue" because you have assigned them the color "blue" on the configurable product and/or simple products.
If you have a configurable backpack with four colors, make sure the configurable product does not have any color assigned and assign respective colors to the the simple products.