Hi Alex..this subject pops up at least once a month..lol..
Yep, it's normal for PL flowers to look green. Someone once said this happens when a plant is older..
How old is your plant?
Don't worry about its color..I like white flowers, but green is nice, too..Since your plant is blooming you're doing something right..Right? Toni

Sorry if it comes up often, I didn't see much from a brief search of the forums. I'm not sure how old the plant is, we bought it fully grown.

However, my wife just noticed probably around a hundred or so brownish millipedes crawling around the soil. Wikipedia says they eat decaying/dead plant matter, so I suppose they're a sign of root rot?

Yikes! Better get rid of those millipedes before they atart nibbling on the roots! They did that to a braided ficus of mine (hundreds of them) Then they had tons babies! I lost the top half to one of the five trees, so I ended up with five braids, four trees!

No it's not a sign of the plant rotting. They eat the decaying organic matter that's in the soil, well, until that runs out, or they want to try something new like a toot salad!

If you don't like chemicals, you can either, take it back to where you bought it and get your money back, or, change the soil (outdoors in the shade) and replace with new soil, or, when it's time to water your peace lily, take the whole pot outside and place it in water deep enough so it comes up over the rim and floods the soil.
You can use some type of bucket, tub, or a childs pool. Anything that will hold enough "tepid"water to come up over the rim.
Then just leave it there. Maybe 15-30 minutes or so, those buggers should come floating up to the surface for air, then you can just dump them out. Might have to do that a couple of times.
Replace any soil lost in the "flood".

Billy Rae

If you're going to flood the plant to force the millipedes out, I would suggest going past the 15 minute mark with these nasty things. The last time I had to carry out this chore, I soaked my plant for 15 minutes. Well, much to my dismay, none of the millipedes surfaced; the buggers survived! The next day they were poking their vile heads out of the soil, sticking their tongues out at me... So I took the plant out to the yard, replaced the soil and bid them adieu forever... Perhaps Billy Rae's suggestion to repot may be best!

Put a few drops of dish soap in the water. This iritates the millipedes and they'll be more likely to come out.