$Sheet->Cells(22,31)->{Interior}->{ColorIndex} = 6;

##</code><code>##

$Sheet->Cells(22,31)->{Interior}->{Color} = $Excel->RGB(255,255,0);

##</code><code>##

$Sheet->Cells(1,1)->{Interior}->{Color} = ($blue << 16)
                                        + ($green << 8)
                                        + $red;