I put Garlemald itself as being of a Mardu (Red/White/Black) bent. All individuals need not adhere to this philosophy, however; Varis strikes me as being closer to Esper (White/Blue/Black) in terms of alignment. Either way, Garlemald has consistently shown itself to be more concerned with its ruthless ambitions than whether or not its ambitions are good for anyone else (or even itself in the long run), so it has Black in the mix no matter how you slice it. It also has no concern for the natural world (beyond as something to rule) and a deep love of machines, so it has no Green. Ergo, the only alignments it falls under is Mardu (war is glorious, conquer whatever you can, disregard the cost) or Esper (calm, calculated, rational decision making to improve the world - this does not necessarily belie heroism, however).
Again, individuals can differ from their country's ethos. Gaius is presented as straight Mardu, but Regula is presented as Boros (Red/White - lacking Black's amorality and ambitious ruthlessness), while Zenos is presented as Rakdos (Black/Red - lacking White's desire for order in pursuit of his own selfish desires - or maybe he's Sultai. /shrug). As a sovereign nation, however, Garlemald has consistently shown the amorality, ruthlessness, and ambition of Black. Not all citizens agree with everything Garlemald does, but their nation still follows this course. (Or: not all US citizens thought going to war in Iraq was a good idea, but it still happened.)
A key thing to remember when discussing Magic philosophy is that no color is inherently good or evil - not even Black. Taken to extremes, however, this tends to happen - even White, ostensibly caring about the community and order, can be evil by mandating the sacrifice of individuals for the greater good and repressing freedom.