erc-header-line-face-method

erc-header-line-face-method is a variable defined in `erc.el'.
Its value is

nil

Documentation:
Determine what method to use when colorizing the header line text.

If nil, don't colorize the header text.
If given a function, call it and use the resulting face name.
Otherwise, use the `erc-header-line' face.

You can customize this variable.