to wear similar colour/style dress as bridesmaid to BIL's wedding?

[lovessummer]

So here?s the background:
BIL is getting married, DT?s are page boys, DH is a best man, FIL is wearing the smart hired suit that all the main men are wearing, MIL had a personal shopper for her outfit. DH and I don?t have much money and all my friends are now married, so cannot foresee another time when I will need a smart dress. But I realise if everyone else is so smart, I don?t want to look like the poor relation. So I spent last weekend going round the charity shops and after trying on loads of unsuitable dresses I found a gorgeous Monsoon one. It fits me perfectly and I feel great in it. But big problem- it is virtually the same colour as the bridesmaids dress and similar style too (i.e. strapless, floaty and knee length). So is it bad form to wear a dress similar to the bridesmaid and/or if I do end up wearing it, am I going to feel like the awkward old matron in it compared to the young attractive bridesmaid? But the wedding is in 4 weeks and I really don?t think I have got the energy to start all over again?

Even if you didn't know the colours, so it was totally innocent, people would still raise an eyebrow IME.

There must be some very odd people about. I've been to weddings where women have been wearing the same colour as the bridesmaids and didn't give it a second thought, nor do I remember any comments from other people. It all sounds rather precious, and it's utterly ridiculous to think that you have to find out the colour of the bridesmaids' dresses to every wedding you go to so as not to have people thinking you're "miffed" about not being a bridesmaid. Good lord.

Wear something else.

Glad you've found another dress.

Even if the bride and bridesmaids are cool with it, you'd have to decide if you were happy for other guests to be thinking (and possibly saying) "Why is that girl dressed up like a bridesmaid? IS she making a point? Maybe she wanted to be asked?"

Thanks again for comments.
Yes I must admit I genuinely wouldn't have worried about anything that anyone wore to my wedding. But from the overwhelming consensus it seems other people would feel it was a bit odd, which was enough to put me off. I feel anxious enough about it as it is, so I don't want to do anything that might make people comment or wonder. (just for the record I have absolutely no desire to be a bridesmaid!). I am definitely not going to wear the other dress (it wasn't exactly the same design or colour but enough for me to feel uncomfortable). I am sure I will get the opportunity to wear it to something else in the future as am loathe to resell it on ebay as its such a lovely dress. But its a classic design, so it will keep. So two dresses for £20 in total- just about within my budget!