This is an old post. The information it contains is probably out of date or innacurate
This is a post that was written a long time ago and is only being kept here for posterity. You should probably look up more recent blog posts related to the subject you are researching
I recently came across rgba colours which are a very simple and logical way to produce a colour (rgb) with alpha transparency as well. This is ideal if for example you want to create a translucent white box to put some text in.
CSS does have some (dodgy) opacity controls, but they set everything as transparent including any text or pictures contained within the element. By using rgba, we can set a translucent background colour and have opaque elements contained within.