A healthy baby is born Shabbos, בעוד היום גדול.
The only other possibly relevant information might be that both parents are irreligious.
Rabbi paskens bris should be on Sunday.
Explain.

maybe since the parents don't keep shabbos, they assume the baby won't either and don't want to be mechalel shabbos for a bris. just like some post-partum women are told not to do a hefsek on a friday?

That's ridiculous. How does the religiosity of the baby or his parents affect the mitzvah of וביום השמיני ימול בשר ערלתו?

Perhaps the parents insist on things like videotaping so the rabbi figures better to have the bris on Sunday when they can videotape to their hearts' content.

No. The bris will be done in a religious setting.

When you say 'bod' does that mean 'smack in the middle'?

I assume the amount of chillul Shabbos that may be involved (having all the guests drive there and back, carrying, turning on lights, setting up, etc. ) may play a role, assuming it means 'smack in the middle'.

i've never heard of a bris being postponed because the rabbi didn't want the guests to be mechalel shabbos. they're going to be driving and turning on lights regardless, it sounds like an excuse for something else. but what??

Maybe he's afraid they'll be mechalel shabbos for him? For instance, "Here, rabbi, let me turn on some more lights for you."

Depends on baby's color.

From R. Moshe Shternbuch's Shu't Teshuvot Ve-hanhagot volume 1:

http://smg.photobucket.com/albums/v336/mel...nt=scan0004.jpg
http://smg.photobucket.com/albums/v336/mel...nt=scan0005.jpg
http://smg.photobucket.com/albums/v336/mel...nt=scan0006.jpg

Interesting.

I don't think that a mamzer is nimol on Shabbos. Maybe not even a halal.