As per Q ref:

A ship when quarantined, used to fly a yellow flag as 'Caution'.

Now, it's reversed and seen as a signal for clean/ready to sail.

Yellow as all things sun. (blue sky.........blue/yellow)

Masons

Ukraine

Think Greece, and pictures of whitewashed houses with blue windows ...

Or Epstein's 'temple'.

Greek societies. Greek color-scheme historically.

Yellow ochre, earth red, Egyptian blue and black were widely used.

RYB are the primary colors. Y and B make Green, a secondary color.

One of these might work. lol