I read from a delimited file and create a hash of a hash of an array.

See and that exactly is the problem :) Use an AoA and the sort will become trivial.

Update: Of course you can transform the data to an AoA first:

my @data;

for $colour (sort keys %hash){
     for $device (sort keys %{ $hash{$colour}}){
          push @data, [ $colour, $device, $hash{$colour}{$device}[0] ]
+;
     }
}

@data = reverse sort { $a->[2] <=> $b->[2] } @data;
[download]