You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: rainbow.go
    path of file: ./repos/gomuks/ui
    
    the code of the file until where you have to start completion: // gomuks - A terminal Matrix client written in Go.
// Copyright (C) 2022 Tulir Asokan
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option
    
func (rbw rainbowBufWriter) WriteString(s string) (int, error) {
	i := 0
	graphemes := uniseg.NewGraphemes(s)
	for graphemes.Next() {
		runes := graphemes.Runes()
		if len(runes) == 1 && unicode.IsSpace(runes[0]) {
			i2, err := rbw.BufWriter.WriteRune(runes[0])
			i += i2
			if err != nil {
				return i, err
			}
			continue
		}
		i2, err := fmt.Fprintf(rbw.BufWriter, "<font color=\"%s\">%s</font>", rbw.ColorID, graphemes.Str())
		i += i2
		if err != nil {
			return i, err
		}
	}
	return i, nil
}