I used a scarf to make my dress distinctive from my sister who was MOB. We both independently chose nearly identical dresses for her middle D’s wedding. Both were from Macy’s, same style, same royal blue color and fabric. Hers was embellished with rhinestones and similar and mine wasn’t but otherwise it looked like we had planned it. Several of her friends commented on our coordination at the wedding (I could tell sis was NOT pleased tho she smiled), so I artfully tied a scarf on mine so that our dresses looked very different thereafter. Issue resolved.
OP here. The bride has said several times she doesn’t care what color, but thinks shades of blue would be good. When she said her mom switched colors to indigo I bought this one, but when I saw her recently she said it looks Navy. Both dresses are long. Hers is a Lauren Ralph Lauren strapless dress from Macy’s but I can’t find it on the site. Mine was from Dillard’s and is Navy/midnight. Here it is in black:. https://www.amazon.ca/Calvin-Klein-Sleeveless-Evening-Ruching/dp/B075JPRRZM
It really looks flattering and it’s so comfortable!!! I tried on 20 dresses and this was the first one that felt good. No alternate color except black. I’d hate to upset the mob though. She seems very nice, but when I said I’d return mine she didn’t say “oh no, keep it”.
I’m 7 days over the 30 day return period
Love it!
Is she judging the color by this photo?
She says keep it and you love it, keep it and enjoy. Navy IS a shade of blue. It looks like a classic you could wear for other events too, another plus!
I think it looks beautiful. If I were you, I’d keep it.
One would hope the MOB doesn’t want to upset you either. You like the dress, it looks and feels comfortable, and it’s affordable, so I can’t imagine any reasonable person would object to you wearing it. I wouldn’t waste my time worrying about the unreasonable ones.
Keep the dress. It is lovely! And will look very different from a strapless dress the MOB is wearing even if the color winds up being similar.
I love that dress. I think it will be fine. Really.
Love the dress! Absolutely a keeper. 
Ok, I’m going to backpedal on my first response. I went back and reread your post. I was under the impression that MIL had made some remark that You took that she didn’t want you to wear a navy dress. But it seems she never made that comment. But now it seems she was just commenting on HER dress, that it’s navy not indigo. You are worried you have the same color. Is that right? If so, wear your dress for sure. I love the style and the ruching is very nice. Navy’s can be different shades. You’ll be fine.
Stunning, OP. Love it. You’re done.
Great looking dress! If I were you, I might continue to look a bit but if I didn’t find something I liked as well or looked good in, I would reach out to the MOB and simply say that your tried to find another dress in a different shade of blue, but were not able to . I don’t think you have to be unhappy with the way you look on that special day to be in a different color. In the photos, you will likely not be standing directly next to the MOB any way. I can’t imagine her being upset since she was the one that said her dress is indigo. Not sure how much difference there would be among darker blue shades anyway.
I really don’t know what the difference is between indigo, navy, midnight blue and dark blue. IME, any of those terms can apply to any old dark blue.
It’s a lovely dress, if it fits you well and you like it why not keep it? It doesn’t matter if you and the MOB end up wearing similar or the same color dress, the style will be different. It can be so hard to find a nice dress for these occasions, don’t mess with trying to find another one!
I cannot imagine being upset that the other mother was wearing a dress that the same color or–as is more likely–just a similar color. I really can’t. And I don’t think that a comment along the lines of “they call it Indigo but it’s basically Navy Blue” is some kind of coded communication that you should not wear a dark blue dress. It is the equivalent of saying “they call it Gull’s Wing but it’s really a pale grey blue.”
If she didn’t tell you NOT to return it it is most likely because she thought YOU were expressing discomfort and she didn’t want to interfere in your choice of dress.
Keep it! Wear it! Since it is sleeveless, you might want to have some kind of lovely light weight silk wrap just in case it is chilly, anyway.
Believe it or not, I once went to a wedding where the MOB and MOG were actually wearing the same dress, which they had bought from a catalog. But one was petite, and the other was statuesque, and the dresses were different colors, so the dress looked quite different. We actually didn’t realize it until the bride told us privately.
No time to read the entire thread but I absolutely love the dress. I would keep it. As we all know sometimes harder then one thinks to find the right dress…
I love the dress. I would ask MOB/bride if they would mind if you wear it. Then when they say no, problem solved.
My son is getting married in August. I googled the “rules” and supposedly you are supposed to let the MOB get a dress first, not wear white, black, or red. And unless the bride requests it, not to wear the same color as the bridesmaids. My “go-to” colors are navy and black so I am struggling. The MOB is struggling. I am pale, so I don’t feel comfortable in pastels, champagne, etc… I got a dress in charcoal. Which looks good, but it is a sheath dress and now I am thinking I want something more romantic. I am leading towards maroon or plum.
I went out looking for MOB dresses again today. Still not enough spring colors are out and so many of the dresses are heavy with beading or lace or rhinestones. They will be too heavy and too hot for a June wedding. And still too many of the dresses are black or red. I’m looking for pastel. I’ll wait a bit longer. OP, the dress you chose was lovely.
When I was married in the 80s, we asked everyone to choose in the pink palate, dusty rose even, if you will. But MIL, never argued or protested or anything, and showed up in a bright, everybody look at me, teal. That was indicative of her style in life. I cannot imagine getting upset about the colors being too similar!
@TatinG, I’m running into the same problem, only much of my shopping so far as been online, since I live in the middle of nowhere. I have seen some nice spring MOB dresses on BHLDN, Anthropologie’s wedding website. I may drive down to Boston to try them on in person. I need a knee-length dress (morning wedding in August).
@AllThisIsNewToMe , I love that dress!
@Massmomm , you might want to try a few of the dress shops in Portland, such as Tavecchia on Exchange Street.