Lore Questions: Why is Gridania's Flag Yellow, and What do the 'Twin Adders' Mean?

[Seirra_Lanzce]

too much greenish in the green forest. Yellow add contrast to it, is a matter of design choice if i'm not mistaken. Why Yellow? Snake can be yellow too, maybe is because of the Adder that yellow is a colour choice

[Yrusama]

too much greenish in the green forest. Yellow add contrast to it, is a matter of design choice if i'm not mistaken.

This is the most likely choice for all three. An army's banner should be clear and visible against any background.

Thanalan has a lot of pale yellow colors (sand), so black contrasts nicely. Apart from that, Nald'thal (attributed to scales) is the dual-manifestation of life/wealth and death/virtue. Take wealth (gold) and death (black) and you have the Ul'dah flag!

Limsa Lominsa is a sea-faring nation, so the ship flag is obvious. That being said, there is a lot of green in La Noscea and blue on the sea, making Red stand out vibrantly. There are other things one can speculate, as well.
*It's not a trade city, but one of war and bloodshed. Blood is red.
*Limsa Lominsa is on the western edge of Vylbrand, which in turn is to the west of Aldenard. As the sun sets in the west, the sky (and maybe the reflective sea) might turn red.
*edit: Between Vylbrand and the Cieldalaes (islands) is the Rhotano Sea. "Rhot" in Roegadyn means "red", but there isn't a word "ano" or "tano" in the Roegadyn dictionary.

The ironic thing about yellow is that it's also a prominent color for toxicity and biohazards. Sure, some snakes are poisonous, but you'd think a nature loving community would avoid putting such things on their flag.