Anyway, wise Katheryn says: "First, remember that this is not the last party you'll ever have, and making your own jam or envelope liners will certainly be much more manageable when there aren't so many people on the guest list.
Second, learn to edit. Choose two things instead of twelve (not limiting yourself to colors), and you'll find it easy to create a cohesive look, especially when you choose elements that make sense for your wedding's venue and season)."
I tried this approach, by the way, for Christmas cards, deciding to line them because I knew that lining only 20 envelopes would be way easier than lining 85. I gave up after cutting two liners and decided that people simply won't know what they're missing, and I'm okay with that. One thing that I have been doing is relegating DIY projects like growing my own flower favors to the bridal shower I'm selfishly assuming somebody will throw me, instead of tackling that for the wedding itself.
As far as a color palette though, I say, don't go with two colors. Go with a tone. Earthy, jewel, technicolor - whatever. Don't come up with anything so restrictive that you just can't have those invites you love because they don't match your bridesmaids dresses.* Having an inclusive palette actually leads to more cohesion, as long as everything is all in the same family.
How are you editing your wedding to a manageable scale?
*and lets review here: nobody is bringing the invite to the wedding to compare it to your theme or colors. The invite sets the stage, so go with something you love that represents you and your wedding, not something you feel like you have to have because of your color scheme or theme. Within reason. I'm still not using these. But I will, someday, for some kind of aquarium themed party. Because this is not the only party we will ever have.