There may be a threaded cap at the head which holds the oring against the clear cover. Unscrew the head and inspect for moisture. i like to use 200 proof ethanol or pure grain alcohol to clean optics and remove solvents and moisture. Inspect the battery that it is not venting or leaking electrolyte.
It’s hard to tell from the pictures if the surface is wet, but a spectral light distribution (rainbow effect) can be created by surface finish imperfections in the optic or the mold for a plastic optic.
Good luck to investigate this and let us know what you find.