I think that the best example of the color of his eyes is a close up scene in "Brotherhood of the Bell". Near the end of the film there's a close up shot of his eyes just before an encounter with William Conrad.
Also, in "Mr. Soft Touch", John Ireland says to Evelyn Keyes that he has steel grey eyes.
Close-up in 'Four Horsemen of the Apocalypse' they look blue-green. I personally thought he was wonderful in this film, in a role quite unlike any other he had done!
I've seen several movies of Glenn in color. Desperados, The Man From Colorado, Escape From Honduras, Cimmarron. His eyes are brown with green flecks. Very pretty.