The most straightforward approach would be require or Module::Load or Module::Pluggable.

Module::Pluggable would automatically load all modules, while you need to load the modules when using require or Module::Load.

Module::Pluggable allows you to automatically instantiate objects when loading a plugin, and allows easy enumeration of loaded plugins, but for your case, I consider Module::Load or a simple require to be the clearer approach:

sub new_class {
    my $class = shift;
    (my $module = $class) =~ s!::!/!g;
    require "$module.pm";
    $class->new( @_ );
}

my $red = new_class('redObjects', color => 'red');
my $green = new_class('greenObjects', color => 'green');
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