In Chapter 7, Brinker tells Gene that he plans to enlist the next day. Gene is thrilled by the idea:
To enlist. To slam the door impulsively on the past, to shed everything down to my last bit of clothing, to break the pattern of my life--that complex design I had been weaving since birth with all its dark threads, its unexplainable symbols set against a conventional background of domestic white and school boy blue, all those tangled strands which required the dexterity of a virtuoso to keep flowing--I yearned to take giant military shears to it, snap! bitten off in an instant, and nothing left in my hands but spools of khaki which could weave only a plain, flat, khaki design, however twisted they might be.
For Gene, exchanging his "school boy blue" for khaki represented escape from the misery and guilt his life had become at Devon. To enlist meant leaving it behind and freeing himself from his daily torment. No matter what the war would bring him, and he knows it "would be deadly all right," it seems to Gene better than what he experiences every day watching Finny suffer because of Gene's betrayal.
In a more general interpretation, "school boy blue" symbolizes youth and innocence, the boys' lives at Devon before the intrusion of the war: studying, playing at sports, going to chapel. Khaki, the material of military uniforms, symbolizes adult reality. In 1942, that reality was a world war, envisioned by the boys, for example, in their reference to a burning troop ship with oil and fire in the water all around. In the summer of 1942, the war seemed unreal to the boys, something that existed out there in the world, far away from their peaceful campus. By the spring of 1943, it had arrived. Finny was dead and Leper was broken, but Gene left Devon behind, put on khaki, and went to World War II.