Piping a command through a color filter

You'd use tput for that:

tput setaf 1
echo This is red
tput sgr0
echo This is back to normal

This can be used to build a pipe:

red() { tput setaf 1; cat; tput sgr0; }
echo This is red | red

The basic colours are respectively black (0), red (1), green, yellow, blue, magenta, cyan and white (7). You'll find all the details in the terminfo(5) manpage.

Here's a little script that does just that. Save this as color in a directory in your $PATH (for example, ~/bin if that's in your $PATH):

#!/usr/bin/env perl

use strict;
use warnings;
use Term::ANSIColor; 

my $color=shift;
while (<>) {
    print color("$color").$_.color("reset");
} 

Then, pass your text through the script, giving . as the pattern to match and specifying a color:

The supported colors depend on the abilities of your terminal. For more details, see the documentation of the Term::ANSIColor package.

With zsh:

autoload colors; colors
for color (${(k)fg})
  eval "$color() {print -n \$fg[$color]; cat; print -n \$reset_color}"

And then:

$ echo "while" | blue
while