Bitchy Little Boy
... so I can bear with you, please!
Phil Eklund's games are like a bar of gold from a complete stranger.
I have only "translated" the official text:
Any exterior or interior parts of the tile must match any adjacent tiles and the sides of the Construction Yard.
Each side of a tile has two halves which can be the same colour or different colours. They must "match" the adjacent halves of their neighbouring tiles or site "sides". There is no official diagonal requirement.
However, if a half-side of a tile corner is green, the other half-side of that corner must also be green (and the same is true for gray). The colours of the sides of the laterally-neighbouring tiles/site must match. Therefore they must have the same colour. Then, obviously, the half-sides of the fourth, "diagonal", corner must have the same colour. Consequently, the requirement of the rules can be rephrased as:
The corners of the tiles must have the same colour as the corners of the neighbouring tiles or edges of the construction site.