There really isnt much you can do about a liner that is already bleached or faded.
Liners are "printed" with dye and once the dye is faded, then its done.
Isolated spots of fading are generally caused by a concentration of chemicals in that area. Likely the result of adding liquid chemicals too fast or adding them in an area with poor or no water circulation.
In the future though, you should be able to prevent that by adding liquid chemicals by pouring them very slowly in front of a return and let the pump continue to run for at least 30 minutes after adding them, so they get mixed well in the pool.