Found this:
Q: How does chemistry work with FUT Icons?
A: FUT Icons chemistry follows these rules:
The same nationality will have a hyper link (green)
Different nationalities will have a strong link (green)
Icons and non-Icons players with the same nationality will have a strong link (green)
Icons and non-Icons players with a different nationality will have a weak link (orange)
Icons players will at least have a weak link with every player in FUT 19.