Is there a program that formats the output of another programming using custom formatting rules?

I'm looking for a program that can take the output of another program and format it. Say we have A being piped to B. If A spits out a line that B recognizes (based on say a regex match) then it formats it using custom rules found in some configuration file.

Use-case: I want to format the output of tcpdump in a very custom manner with colors.