Hal Jordan's Invisibility & Light Refraction

The power of invisibility is created by the Power ring bending the light waves around the wielder's form, which also brings the ability of creating constructs of a different color other than green, but that's only seen on experienced power ring welders.

Once Hal Jordan became a more experience green lantern corps member and an adept power ring welder, he was able to create illusions of people and objects in full original colors, but that was for the purpose of illusion and bending reality, but when it comes to battle, no ring welder, experienced or not, will focus in making the constructs in a different color rather than green.

Taking this into account, Hal at some point was able to create illusions of his background with full original and faithful coloring, rendering him invisible to the outside eyes.