Inner Space Aliens. Ambassadors of Orealis, #2

Teen ambassadors, aurora-coded warnings, shapeshifters, and a ticking subterranean plan. Fifteen-year-old Erik is tetrachromatic; he can see a hundred million colors, a gift that made him capable of reading the complex language of the Aurora Borealis, crucial in his role as one of Earth's interstellar ambassadors. When an ominous red aurora spells out "war, " he finds himself at the center of a cosmic threat.
Driven by Óðin's messages in the sky, Erik teams up with his fearless twin, Finna, his steadfast best friend, Kalli, and a runaway sculptor with secrets of his own, Erik must unravel the truth behind Iceland's Huldufolk, the shapeshifting Morphyte army led by a three-eyed alien giant, and the planet-tuning Meridian Loki left behind. If Erik and his friends can't stop it, Earth will fall. Erik never asked for the title Óðin gave him, but as the mesmerizing, colorful auroras grow ever more menacing, Erik realizes he's the world's reluctant last hope.
Armed with Finna's arrows and Kalli's rallying voice, the friends discover the uncomfortable truth: saving Earth will cost more than courage. Leadership asks for choices that have no right answers - only the will to choose.