Because you said Neptune, I used actual Neptune to do some quick and dirty math. To have a 30 day orbital period our "moon" has to orbit at about 1,000,000 km. This makes our gas giant have an angular diameter of about 170 arc minutes, or ~ 6 times larger than the moon. This would roughly mean that an eclipse would last about 6 times longer, for a max of about 45 minutes when everything lines up and you're standing in the right place. As for how blue it would make your nights (and, potentially, at least a little bit, your days), use your imagination, I feel like you've got a significant amount of artistic license there.

EDIT: And to add, just in case you don't know, your planet is tidally locked to the gas giant. The above only applies to the gas giant facing side of the planet. The other side will have uninterrupted days and very dark nights. And is probably colder, I think. And gets hit by more meteors.

A more distant orbit would result in a slower orbital period than 30 days. Check every moon in the solar system and in fact the planets themselves. Mercury takes 88 Earth days; Neptune takes 165 Earth years.

Also the orbital period would be thirty hours, not days.
Maybe that would force the moon inside the planet's Roche limit. Or at least inside "we're dead" limit...

Yes. I've been struggling with the necessary label for an iron-age war drama set on an alien planet...dunno I'll figure it out after I've written the thing.

I'm going to second Tom and BDA here. It's more important for the details to serve the story then vice versa. Unless you're writing super hard sci-fi, no one is going to get mad at you because your math doesn't check out. Don't feel beholden to my math and speculation if it's getting in the way of your story. I was going to type more here, but I realized I was just repeating what Tom said in different words, so just go read his post again.

Edit: I will add this: It's ok to tell us about your world, the details you give us help bring it to life, but do it in a natural way, and don't overwhelm us. We should learn about your world the same way we learn that Tattooine has two suns, or that Coriscant is all city. No one sits down to have a conversation about it, it just shows up in an establishing shot and everyone just treats it like it's normal, 'cause to them it is. Those details are an important part of bringing a world to life, Tattooine isn't really the same without it's twin suns, but they're backstage to the story taking place.

....I haven't read a page, and I'm already in love with the concept world we're kinda building here.