Masquerading (sometimes called NAT) can be disabled for the local network zones. That means that packets originating from the local networks are not masqueraded when being sent to the RED network.
Please do not change the default NAT settings unless you have a good reason to do so, i.e. some devices or applications don't work correctly. Usually, you don't need to change the settings if you are operating a home network.
To change the default masquerading settings, access the firewall options page in the WebIF and choose the appropriate settings for your network. Masquerading/NAT can be turned on or off for each network zone.