I agree with dws, OOP definatley seems like it would fit with your project. Plus you could do fun things like overload the stringify operator by adding

use overload "\"\"" => \&as_string;
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to the EmmisiveColor class. Then your simple_properties could become:

sub simple_properties {
    my $self = shift;
    return
       "appearance Appearance {\n" .
       "  material Material {\n" .
       "    ". join("\n    ", $self->properties). "\n" .
       "  }\n" .
       "}\n";
}
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Overloading a string operator might be quite handy for what it looks like you are doing, and I bet you would find other significant simplifications with an OOP approach. Here is a quick overloading/oop tutorial. (shameless self promotion :)