I myself thought a little bit about the Psionics/Light coloring question. I solved the issue for my own mind like this: I consider the Hagah as having additional armor.
The torso piece in particular comes to mind as it is not present in other Toa Metru builds. If you were to design a white and gold Lhikan for example, yes, that would be a Toa Metru of Light. However, if you give this toa an additional torso armor piece, as well as Hagah shield and spear, then it is a Toa Hagah of Ice.
See, the Hagah are a very specific team of elite toa. The way I see things (I might be wrong though) is that the Hagah are the only toa team to have that much armor. Only the Nuva have a similar amount of armor but they are also one of a kind in the Matoran Universe, and they don’t have the Hagah shield anyway. There is no Toa Hagah of Psionics or Light, this is a fact. The special elite metallic additional armor and weaponry are specific to the Hagah. Therefore, it is not possible to see a Whilte/Gold or Blue/Gold Metru build moc and wonder whether it is a Toa Hagah of Ice or a Toa of Light/Psionics. There is no overlap on their design. The presence of the elite additional armor and Hagah weaponry will make it obvious if it’s a Hagah and, therefore, Ice/Water, or if it’s a toa of Light/Psionics.
My point is that there is nothing wrong with someone designing a Gold Gaaki or Kualus. They wouldn’t break the canon IMO since their “basic” armor color would be White/Blue, only the “additional” Hagah armor would be metallic and, as such, they should not be disallowed.
I probably will only vote for silver entries, but I see no real reason to forbid Blue + elite Hagah Gold armor and White + elite Hagah Gold armor as that is different from Blue/Gold and White/Gold basic armor IMO.