use strict;

my @file = <STDIN>;
my $word = "color:";  # no space after colon

for my $lineno ( 0 .. $#file ) {
    if ($file[$lineno] =~ /\b$word\s*(\w+)/){ # notice the capture brackets
        my $value = $1;   # $value here is 'red'.
        ...
    }
}