Though there is not any kind of live color feature implemented in inkscape, there is an easy way to do such behaviour in inkscape. Create a new gradient, name it whatever you want and then open the XML editor. Expand the svg:defs element, click on the apporiate gradient you've created and remove one of the stops, so there is only one stop left. If you need, set the opacity of the stop in the gradient dialog to 1 and then choose your color. Create objects and assign their fill to that gradient. Then change the color again and voila - you will ha a such feature.

Another way to do this is to open the xml editor, create a svg:style element with type "text/css" and create a class element with a special fill color. Assign it then to any object you want to affecct with the class definiton. Doesn't works in inkscape, but works in svg readers. Some thoughs about this cool behaviour.

This tip has been posted before (but it's a goodie). You might be interested in reading the dicussion that followed - viewtopic.php?f=6&t=248#p1362

Are your referring to naming the gradient in the xml editor or is this possible another way?