You could use the built-in capture variable $1 to extract the word next to the one you are after -

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 bra
+ckets
        my $value = $1;   # $value here is 'red'.
        ...
    }
}
[download]

Another possible variant, say, in case there are multiple color attributes on the line, you want to capture all of them in an array.

my @colors = $file[$lineno] =~ /\b$word\s*(\w+)/g;
[download]