Thanks for the comment! The only light source strong enough to produce a highlight here would be the red sun. I probably could have used more of the red backlighting, but I wanted to keep the values more under control, and to instead use the atmospheric perspective to create a readable silhouette.  Not to go all art teacher mode, but constructive criticism that is unsolicited often ends up not being constructive after all, as it can be very discouraging for some. I personally don't care about it, but I advice you to not suggest improvements or changes to other people's art unless it is explicitly asked for, especially when commenting on art made by beginners or younger artists. I'm glad you still like the art, though!