Metroid: Father Hunt

[Gors]

This is unrelated now that you already found a way around the portal, but the green highlight in the first Metroid's portals were not made to make a connection with Samus' missile shot. It is purely an effect of the NES limitation: when one color is changed in the sprite palette, it affects everything that uses it. Samus and the door happen to share this color, and therefore, when you change it, the door also changes. Another example of palette cycling happens in Legend of Zelda. When Link uses a green robe, the fast palette cycling enemies (such as Zora's fireballs or those electricity balls that roam in dungeons) will use the same green in the animation. Oce you get a magic ring and your robe color changes, the mentioned sprites will also change color.

It's interesting that even if in Metroid's case, it was purely a design limitation, you can infer this secondary meaning that 'the red doors have something to do with missile shots'. This is great game design imo.