Kryptonite is green.... Can the Green Lantern defend himself against Kryptonians? Or can the ring not make something that acts sufficiently like kryptonite?
The Green Lantern rings are capable of creating Kryptonite and Kryptonite Radiation because the rings are capable of Energy Projection and can therefore mimic certain types of materials and energy signatures.
Energy Projection: The ring can be used to fire blasts of Oan energy or create weapons such as projectiles of them. The ring can project beams of force powered by the will of the user. The ring can be used to produce kryptonite and kryptonite radiation.
DC Comics Presents Vol 1 26