Of note is that with line charts, there are several different places where colour options exist. The colour of the line, the fill colour of the markers, and the outline colour of the marker. All can be set independently of each other. In this example I just set them to the same thing, but if you want them to be different just supply different rgb byte arrays when setting them.
CTChart ctChart = chart.getCTChart();
CTPlotArea plotArea = ctChart.getPlotArea();
CTLineChart lineChart = plotArea.addNewLineChart();
lineChart.addNewVaryColors().setVal(false);
CTLineSer lineSeries = lineChart.addNewSer();
lineSeries.addNewSmooth().setVal(false);
byte[] color = new byte[] {(byte) 195, (byte) 224, (byte) 176};
CTShapeProperties lineProp = lineSeries.addNewSpPr();
CTSRgbColor fill = lineProp.addNewLn().addNewSolidFill().addNewSrgbClr();
fill.setVal(color);
CTShapeProperties markerProp = lineSeries.addNewMarker().addNewSpPr();
markerProp.addNewLn().addNewSolidFill().setSrgbClr(fill);
markerProp.addNewSolidFill().setSrgbClr(fill);