select and edit multiple data points, graphs in one chart

Hi,
I have a chart with 10 different Y data series and one x data series. Points are linked together with lines for Y1, and another graph for Y2 and so on. Y1 lines are colored as red, Y2 as blue, and so on in different colors.
I can change the color of the first graph Y1 by selecting this and changing the line color to black. I can change the color of the second graph Y2 by selecting this and changing the line color to black. And I can do so until I got mad.
Can someone expert tell me how to select all the graphs and just change the color in one step for all my series?
I would appreciate your help.