How is the topology of your network? Physical or virtual? If the former, are all your switches working properly, If the latter, are you correctly routing the virtual network? You might discover that your problem is not IPFire configuration at all but something outside its domain. To test this hypothesis I would connect directly to IPFire green interface one machine and the same to the orange assigned ethernet card so to simplify the system. Also, I would make sure as mentioned by @luxskywalker that is not the routing inside your green machine or orange machine the problem due to a local firewall rule. Finally, are you messing with the ICMP traffic?
Check also the arp table in all your machines (also route command can be helpful), maybe you can figure something out from there.