This does allow light to come in, so not room darkening. The back is white. The print does line up pretty darn close (Only a little bit on the top was not quite evenly matched between the two panels.) The photo attached was taken during daylight hours, so you could see the transparency. I purposely lined the panels up so the darker 'ground' was lower than the window frame, this doesn't get the sunlight shining through it.  Yes, you do see the seams, which will break up the pattern in the muddle, but that is to be expected. Normally you'd want curtains at least a third wider than the window, but because of the print, you'll want to get as close to actual window length as you can, so there isn't as many pleats/folds. The colors of this one go perfectly with the colors of my room. I've only had these up for a short time, so I can't comment on the longevity of them. So far I love them!