Got to agree that if you just want to light up a background with color you want a
cyc and not a
scrim. Furthermore I've got to put my vote in for a white
scrim. I've used blue and had a hard time with things turning green the first time you
spill some amber or yellow light on it. In an
amateur setting where you don't have a lot of instruments, it's much easier to use white. If you're worried about having a giant white wall there the whole time another option is a grey
scrim. It's harder to get a good bright punch out of, but it's not as bright the rest of the time and still picks up colors well.
As for lighting, yes you want to use as extreme
flat angles as you can get on it to make it appear solid. Front light will allow you to see through a little. If there is ANY backlight you will see through. One trick many people use is to have another drape right behind the
scrim of the same color to ensure that it looks solid. When it's time for the big
reveal effect you fly that drape out at the last second.
True you can use a white
scrim as a
cyc... but you better have something behind it just in case because you will probably see through a little.