I have looked through the sample sparklines, and also through the source code. There does not seem to be a way to change the line color. My page uses a black background, and I will to use a light color for the line.
Am I missing something? Or has this fucntionality not been included yet?

I haven't been able to find this, either. It seems kind of ridiculous that something so basic is either impossible to find or impossible to do.

It is hardcoded. Search for 'black' in Sparkline_Bar and Sparkline_Line