This is the fundamental conflict between Rangers and Druids. Druids are Green-centered, and just as likely to be Green-Red or Green-Black as they are to be Green-White or Green-Blue. Rangers are fundamentally Green-White, even leaning White-Blue at times.
translation for someone who doesn't speak MtG colour-alignment jargon please?
Green is the color of Nature (Instinct and Interdependence on the chart here). Druids are almost always some version of Green. Often they are pure Green, but you can often find them with other colors mixed in.
White is the color of Order and Morality. On its own, you'll usually see knights, soldiers, angels, and the like in White. Green/White is fairly common, which would be "peaceful/ordered nature". Think things like agriculture both in the form of fields and orchards, or communes seeking to grow stronger together.
Red is the color of Impulse and Chaos. Red is often destructive, and is the color of (Magic's particular flavor of) goblins, fire, earth, barbarians (though I think Magic uses "Warrior" as the creature type nowadays), and dragons. A red/green card would be a more aggressive take on nature. Green/White is nature harnessed, Green alone is nature which just wants to be left alone to do its thing, and Green/Red is nature going out to pick a fight.
Blue is the color of Logic and Technology. Blue is the color of trickery, knowledge for its own sake, and artifice, all things Green isn't particularly fond of. When you do find Blue/Green, they tend to be flavored around artificially altered nature, or someone delving into nature's mysteries.
Black is the color of Parasitism and Amorality, and often seen as the color of Death which is opposed to the Life-centered view of Green. Black has things like various undead, greed, life-drain magic, and a willingness to "do what must be done". When you do find Black/Green cards, they tend to be focused on a "cycle of life" kind of thing: things die and then give rise to new things.