I'm not 100% sure, so perhaps other teachers will comment, but here's what I think:
glow on = caused by something external
"As he approached the end of the tunnel the first thing he noticed was a slight glow on his skin."
glow to = caused by something internal
"The yellow glow to his skin and his eyes told me that the problem was his liver."
I do think there is a sort exception to this rule (the rule I created above), because people often use 'glow to' when the glow is caused by some sort of tanning product or process... is that internal or external? I don't know. I'm not a scientist. I think people choose 'glow to' in this context because it seems more natural... maybe?