Speculation,
Fortifications:
Jaguar temple (blue)
Defence buff when fighting off a siege (likely similar to GvG siege armies).
Blue is the designated colour in the game for defending armies and their bonuses. The jaguar temple is blue too. Making it somewhat sense that it relates to defence. Besides that new mechanics seem to playing a role with defensive bonuses.
Eagle temple (red)
Attacking bonus buffs when attacking a new encounter, or additional buffs to friendly besieging armies.
Red is the designated colour of attack bonuses. Thus it making sense that it's attack related. Besides that, although unlikely to relate in any way, the eagle mt. Reserve buffs attacking armies.
Warrior temple (green)
Jack of all trades, buffing both friendly besieging/invading armies as friendly defending armies while fighting off a siege army.
Green has no known designation related to armies in FoE. However in Grepolis there's a distinct ranking list known as warriors. While top attacking and defending player rank exist too. The warrior ranking taking both aspects into consideration. Although not a perfect parallel, it makes sense that the warrior temple will be a jack of all trades. Buffing both offensive as defensive armies. While likely giving a smaller bonus for each army compared to their respective dedicated army.
Statues, for each statue it's likely the same for each respective colour. However instead of buffing armies it'll likely assisting for those who prefer negotiations over fighting. It kinda makes sense. A statue to charming those with who you're negotiating, while in temples your armies finding inspiration to keeping their moral high.
All of this is just speculation but I think it makes the most sense. It'll also give a reason to constructing defensive GB's and likewise event buildings. It's just a thought of how the devs maybe attempt to making defensive buffs relevant (again).