Background (see https://greenlantern.fandom.com/wiki/Emotional_Spectrum#Blue.2FHope):

Blue is a color close to the center, and represents the emotion of hope. The blue light is capable of being wielded by a being who can bring hope for the future to others. The blue light is the most powerful of the spectrum, but it is also the most difficult to wield and understand. The exiled Guardians Ganthet and Sayd were the first to harness the blue light, forming the Blue Lantern Corps, a force which would assist the Green Lantern Corps in its coming trials during the War of Light. Despite being the most powerful color, it may only function to its fullest effect in the proximity of the Green light (hope on its own is hollow, requiring will to make it reality). The blue light is capable of draining the yellow light, suppressing the orange and red, and empowering the green.