These green panels darkened our room significantly.  I think whether they are truly room darkening or not depends on what time of day/whether they face the sun.  In the morning, when our western windows aren't getting sun, there is almost no light shining through.  Only around the edges.  In the afternoon, it's not quite as dark, but still very helpful.  I would highly recommend them.  They are also awesome because of how easily the grommets slide up and down the rod.  I would never buy another type of curtain again (w/o grommets).  I really like these.  In fact, since redecorating, I'm going to get them in another color.

Color: We got the green.  They are a pea green color (slightly yellow, medium green)

Pros: Dark, slide easily