Until I started sewing, I don’t think I ever owned a white dress. I think that was mostly due to fear: equal parts of ‘what if I get a dirty mark on it’ and ‘what if my underpinnings show through’. One of the great things about making your own clothes is that you can select white fabrics that you know to be easily machine-washable and totally opaque. Now I have two white dresses, both made out of fabric that is all but bullet-proof.
But I also have a length of white polycotton in stash, waiting to become white dress number three. It’s definitely washable. But while it’s certainly not obviously transparent, it’s not opaque. When I lay it on a light brown background you can easily see the difference between two layers of the fabric and one.
You can even see a difference between two layers and three. The seam allowances on anything I make out of this are going to be very visible.
I wondered if this was just a particularly awkward fabric but I had a quick look at a few others in John Lewis and all the white cotton wovens are like that. I think I’ll probably get away with it for the dress I have planned. For one thing it’s completely lined so I can use an opaque white lining. For another, all the seam allowances are pressed to one side and double-topstitched, so the seam allowances will just add to the emphasis.
Maybe the effect is less obvious on a finished garment? Presumably it makes a difference what seam finish you use. I don’t own any ready-to-wear clothes made out of similar fabric so I haven’t got anything in the house to compare with. If you’re wearing white over the next few weeks and find a crazy woman staring at your garment seams, that’s probably going to be me!
Catherine Daze's Blog 
I think you shouldn’t worry about it too much, the garment will be in movement as you wear it, so it will not appear as see-through
Your right, I think it does depend on the patter a little so I think it will be fine with lining. What pattern are you going to use?
You could always underline it if you wanted to make it totally opaque. Or make a shirt, for some reason I don’t think it matters on tops if you see the seam allowance, I guess because we are so used to it?
I have a white linen blouse with princess seams and the visibility of seams annoys me – especially when I haven’t done a great job on the ironing. It shows. Your fabric seams quite slight for a dress, so Alison’s underlining suggestion is worth considering.
I would definitely go with the underlining, even if you make up a shirt. I personally have a strong dislike of seeing seam allowances on white garments, even if it is something that we see quite often, like Allison says. I just think people will notice the *whole* garment, not the “oh, it’s a white garment – I can see the seam allowances” thing.