So, here is the whole program in case it may prove useful to others:

#!c:\perl\bin
use strict;
use OLE;

$Win32::OLE::Warn = 3;    # Die on errors.

# Start an instance of the Excel application
my $excel = CreateObject OLE "Excel.Application";

# Make Excel visible or not
$excel->{visible}=1;    # 1=True, 0=False

# Create a new workbook (Excel file)
my $workbook = $excel->Workbooks->Add();

# Create and name a worksheet
my $worksheet = $workbook->Worksheets("Sheet1");
$worksheet->Activate();
$worksheet->{Name} = "Color Scale Example";

# Put some values in a range of cells in Column A
$worksheet->Range("a1")->{Value} = 87;
$worksheet->Range("a2")->{Value} = 74;
$worksheet->Range("a3")->{Value} = 16;
$worksheet->Range("a4")->{Value} = 24;
$worksheet->Range("a5")->{Value} = 48;

# Select the cells with the values to be color scaled
my $selection = $worksheet->Range("A1:A5");

# Add conditional formatting
my $formatConditions = $selection->{'FormatConditions'};
$formatConditions->AddColorScale({ColorScaleType=>3});
$formatConditions->{$formatConditions->{'Count'}}->SetFirstPriority;

# Set the color scale criteria which has three components
my $colorScaleCriteria = $formatConditions->{1}->{'ColorScaleCriteria'
+};
$colorScaleCriteria->{1}->{'Type'} = 'xlConditionValueLowestValue';
$colorScaleCriteria->{1}->{'FormatColor'}->{'Color'}=8109667;
$colorScaleCriteria->{1}->{'FormatColor'}->{'TintAndShade'}=0;

$colorScaleCriteria->{2}->{'Type'} = 'xlConditionValuePercentile';
$colorScaleCriteria->{2}->{'Value'}=50;
$colorScaleCriteria->{2}->{'FormatColor'}->{'Color'}=8711167;
$colorScaleCriteria->{2}->{'FormatColor'}->{'TintAndShade'}=0;

$colorScaleCriteria->{3}->{'Type'} = 'xlConditionValueHighestValue';
$colorScaleCriteria->{3}->{'FormatColor'}->{'Color'}=7039480;
$colorScaleCriteria->{3}->{'FormatColor'}->{'TintAndShade'}=0;
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