My quick look at PPT's help got me this VB example:

With myDocument.Shapes.AddShape(Type:=msoShapeRectangle, _
        Top:=144, Left:=144, Width:=72, Height:=72)
    .Name = "Red Square"
    .Fill.ForeColor.RGB = RGB(255, 0, 0)
    .Line.DashStyle = msoLineDashDot
End With
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Which is not exactly in line with yours, but is close enough for MS work.

What caught my eye is the use of a VB function cleverly called RGB. Referencing the docs, one finds function RGB converts three arguments into a LONG representing the color. Here's a snippet from my VB's immediate window test cases.

print RGB(0,0,0)
 0 
print RGB(255,255,255)
 16777215 
print RGB(255,0,0)
 255 
print RGB(0,255,0)
 65280 
print RGB(0,0,255)
 16711680
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This function, at least, seems to perform as documented.

Armed with this knowledge, I constructed a Perl example that strives to curve-fit the MS function.

sub RGB {
  my ($red,$green,$blue) = @_;
  return $red + 256 * $green + 65536 * $blue;
}

print RGB(0,0,0) . "\n";
print RGB(255,255,255) . "\n";
print RGB(255,0,0) . "\n";
print RGB(0,255,0) . "\n";
print RGB(0,0,255) . "\n";
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As you can see, the Perl function fits the VB data well within the expected error.

0
16777215
255
65280
16711680
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There is no guarantee that our Perl port of VB's RGB function will solve your problem, but it should provide a good jumping-off point.

<Oobject name="tongue" method="in-cheek" comment="intended with best regards =)"/>