The code uses splice to remove the elements from the array but the size of the array is not adjusted in the foreach loop. Below code would traverse the array based on the last index of the array. This works even after using warnings module without any error. Here I am adjusting the for loop count based on your splice.

use warnings;
print "hello world\n";
my @colors = qw(red green blue yellow pink purple brown);
my @drop = qw(pink brown);
my $num = 0;
for (0..$#colors){  
    
    if ($colors[$num] eq $drop[0] or $colors[$num] eq $drop[1]){      
+   
        splice (@colors, $num, 1);
        $num--;    
    }
    $num++;
    
}
print "@colors \n";
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