Prewash Crepe Back Satin?

I am about to start on a dress using crepe back satin and can't make up my mind whether to wash the fabric or not.  I used crepe back satin a few weeks ago for my nanny's wedding dress and pre washed it according to the care instructions but I have a lot of natural light in my craft/sewing area and as I was cutting it and working with it I could see the differences in color in the fabric...they were really large patches.   I didn't look at it that closely before I washed it so I am not sure if that is just how the fabric is...you can't see the patches unless you are looking at it on an angle in very bright light.  and the fabric I am using now is black and it is very dark and cloudy today so I can't tell.  I really need to get started because I have to have it for Thursday morning and I will be taking pics of it outside if the weather allows so I really don't want to mess it up.  but it is for a child so I know it will need to be washed in the future...sorry dry cleaning to me just doesn't work!  I would really apprieciate any input you could offer.  Thanks!

I wouldn't wash it. The only reason to wash for this project would be if you noticed a significant amount of shrinkage from that other piece.