I've done a project or two with EL wire.
The commercial wire that I've dealt with uses a phospher that is aqua (greenish-blue) in color. If you want to get a different color, you encase it in a colored plastic jacket. The brightness of the wire and how good the color looks will differ based upon how close the desired color is to aqua; green and blue look pretty good and are fairly bright; red doesn't look very red and isn't very bright.
Brightness is all relative; if you are used to the amount of light given off by decent LEDs (not even the high-brightness LEDs), you will think EL wire is dim. My project was a holiday light display (a juggling snowman), which looked great in a dark room, not great when competing with light from other displays.
The ultimate brightness is limited by the breakdown voltage between the inner core wire and the spiral corona wire. If you drive the EL wire segment with too much voltage, you will burn through the plastic, and the segment will be permanent off.
There are now some LED alternatives that look a bit like EL wire; if you search for "neon LED rope light" you'll find some of them. They aren't cheap, however.
BTW, if you are interested in dimming EL wire, there's an article here.