GR translation: lighted from inside like ice

[Mike Jing]

V460.18-23, P468.3-7   One of them has produced a huge meat cleaver, and is
winding up all right, amid much vivacious laughing, at about which point
somebody grabs hold of Slothrop’s ankle. He looks down, observes sticking
out a porthole two slender wrists in silver and sapphires, lighted from
inside like ice, and the oily river rushing by underneath.

What does "lighted from inside like ice" mean here?