Got my striped sheer for Um today!!!
As the ebay auction listed, it definitely is an off white...almost beige...but the stripes are definitely white and in contrast to the red and black fabric when layered, it looks just fine! Thank goodness.. As long as I don't layer or gather it too heavy it shouldn't be very noticeable. The fabric is perfect though and the size of the stripes is perfect too. I can put 5 white stripes in between every 2 black ribbons.

... yes, I'm insane, I know. Who COUNTS the stripes?
I think the off white will be a little more apparent than I'd like on the bodice, however the bodice also has a pink gradient anyways so then again it may just be apparent on the back...which will be covered by hair anyways!
Here's a photo of it on top of the red/black...left is single and folded once over, inset is contrast on black, center is gathered ( the whole 120inches in a ball lol ) and right is contrast on a dirty white box...lol I think the black ribbon will help the contrast too. I'll probably make a mock up skirt and see if it's REALLY bad when it's all together and report back.
I may try to bleach a sample and see if it lightens up the off white a bit...so I'll post back after that.
But for $10 I think I can get away with it. If not, I'll keep on hunting since I have no deadline for Um and it's just a spare-time project. Oh, but it's also real drapery fabric so bonus points for authenticity. XD