I thought she hated me. :c

For tight dresses, I use a poly-spandex. Sloth's dress has what looks like a wine sheen to it. It's red, in some light, and purple, in others. Going with a fabric that gives off one of those colors would be great. When going fabric shopping, take a digital camera with you. When you find a fabric you like take two pictures of it. One without and one with flash.

The first time I made Hinata's jacket, I used lavender dance fabric. The fabric looked accurate but when photographed with flash looked blue. Too blue. I'm a perfectionist... so I couldn't have that. I went out and bought some lilac fabric. I loath lilac because it's purple with pink in it and not purple with blue in it. I used leftover fabric from my first jacket to line the inside of my new one. Now, when photographed with flash, my jacket looks accurately lavender. I don't know if it's the lilac turning so or because I have lavender under the lilac... Anyway... because it doesn't look very lavender without bright lights I want to remake it a third time with fabric that is the right color at all times.

For your dress... I'd say go with a type of spandex, a dull satin, like you came up with, or a velvet that doesn't look like it's too much. I think, your dress will come out very elegant and pretty. I don't know much about formal dress fabrics, because I don't work with them. You could go take a look at prom dresses and find out what fabrics they are made out of.

Now... I'm wondering what to make Envy out of. His clothes have a blue-like and purple sheen... but I don't have a lot of money to spare for him... so I'll, probably, use some spandex. Easier to move around in. Fortunately, I have purple contact lenses (I stock up on these for my Hinata xD)! So one thing will make up for the other.