Have you attempted to read the OLE doc? The answer is a smidge obfu'd but I would like to think you at least tried. However, have a look at the Color propery of the Interior object. A Series contains an Interior property. You can set it there

more info can be found here:
http://www-106.ibm.com/developerworks/linux/library/l-pexcel/
http://homepage.tinet.ie/~jmcnamara/perl/WriteExcel.html
or in the docs of Spreadsheet::WriteExcel

kind regards,
teabag

use strict;
use Win32::OLE;
use Win32::OLE::Const 'Microsoft Excel';

# Start Excel and create new workbook with a single sheet
use Win32::OLE qw(in valof with);
use Win32::OLE::Const 'Microsoft Excel';
use Win32::OLE::NLS qw(:DEFAULT :LANG :SUBLANG);

my (@Names);

$Win32::OLE::Warn = 3;

push @Names, ['loy', 13];
push @Names, ['toy', 12];
push @Names, ['mccoy', 05];
push @Names, ['roy', 47];
push @Names, ['loy', 24];
push @Names, ['toy', 05];
push @Names, ['joy', 24];

print "Start Excel\n";
my $Excel = Win32::OLE->new('Excel.Application', 'Quit');
$Excel->{Visible} = 1;
$Excel->{SheetsInNewWorkbook} = 1;
my $Book  = $Excel->Workbooks->Add;
my $Sheet = $Book->Worksheets(1);
$Sheet->{Name} = 'DepOne';

my $Range = $Sheet->Range("A1:B1");
$Range->{Value} = [qw(Name Hours)];
$Range->Font->{Bold} = 1;

print "Add data\n";
$Range = $Sheet->Range(sprintf "A2:B%d", 2+$#Names);
$Range->{Value} = \@Names;

print "Create chart\n";
$Sheet->Range("A:B")->Select;
my $Chart = $Book->Charts->Add;
$Chart->Chart->ChartWizard({Source =>$Sheet->Cells(15)});
$Chart->{ChartType} = xlColumn;
$Chart->Location(xlLocationAsObject, $Sheet->{Name});
# Excel bug: old $Chart has become invalid now!
$Chart = $Excel->ActiveChart;

# Add title, remove legend
with($Chart, HasLegend => 0, HasTitle => 1);
$Chart->ChartTitle->Characters->{Text} = "Department One";

# Fat candles with only 5% gaps
$Chart->ChartGroups(1)->{GapWidth} = 5;

sub RGB {
    my ($red,$green,$blue) = @_;
    return $red | ($green<<8) | ($blue<<16);
}

# White background with a solid border
$Chart->PlotArea->Border->{LineStyle} = xlContinuous;
$Chart->PlotArea->Border->{Color} = RGB(0,0,0);
$Chart->PlotArea->Interior->{Color} = RGB(255,255,255);

# Add 1 hour moving average of the Close series
my $MovAvg = $Chart->SeriesCollection(4)->Trendlines
             ->Add({Type => xlMovingAvg, Period => 4});
$MovAvg->Border->{Color} = RGB(255,0,0);

$Book->SaveAs('somefile.xls');
$Book->Close;
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