Hello and thanks for using Petco Pet Education Center, formerly Petcoach! When there has been inflammation in the skin (like what happens secondary to a flea bite) the skin will sometimes change color as it heals. That area looks like it is starting to regrow hair and that the original inflammation is subsiding so I wouldn't be concerned. It is recommended to use at least 4 months of consistent flea prevention to fully eradicate fleas or all year round if Lynx is an outdoor cat. A high quality flea preventative like Frontline plus, Revolution or Advantage should be used.