Once you have set your series, you can call the method chart1.ApplyPaletteColors() and then check the series[].Color property to determine the color.
chart1.Series.Clear();
chart1.Series.Add(new Series());
chart1.Series.Add(new Series());
Color series1Color = chart1.Series[0].Color;
// Above (Series 1) currently holds {Color [Empty]} || {Name=0, ARGB={0,0,0,0}}
Color series2Color = chart1.Series[1].Color;
// Above (Series 2) currently holds {Color [Empty]} || {Name=0, ARGB={0,0,0,0}}
chart1.ApplyPaletteColors();
Color series1AfterColor = chart1.Series[0].Color;
// Above (Series 1) now holds {Color [A=255, R=65, G=140, B=240]}
Color series2AfterColor = chart1.Series[1].Color;
// Above (Series 2) now holds {Color [A=255, R=252, G=180, B=65]}
These colors will vary depending on the color palette you have set.
To see what color palettes you can set, you can see Alex Gorev's Weblog.

(source: msdn.com)
Source - Alex's blog
He has very helpful posts on .NET charting and I have consulted his blog often, usually from searching for answers to charting questions on google
http://blogs.msdn.com/b/alexgor/
Let me know if this does not answer your question enough to complete your task and I will elaborate on any area you ask that I am capable.