Allow extra_remarks that are colored by severity

I want to emit an error message that highlights multiple disconnected locations in the source as the origin of the error.  I can underline all the locations by adding all but one of them to `extra_remarks`, but the "extra" ones don't get colored red for an error.  Would it be possible to add a way to indicate that an "extra_remark" is part of the error and should also be colored?