It doesn't matter where your template string comes from, it's still a string containing some markup.

It's the same question with the same answer: use a templating system. Consider:

use warnings;
use strict;

for my $color (qw(green blue red puce)) {
    my $text = "The color is COLOR\n";

    $text =~ s/COLOR/$color/g;
    print $text;
}
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prints:

The color is green
The color is blue
The color is red
The color is puce
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