Order By Category

Hi I’ve created an authors page which consists of the author details, and the title’s of the posts they’ve written.

The following code organises the posts alphabetically for me

<?php
$posts = query_posts($query_string . '&orderby=title&order=asc&posts_per_page=-1');
if (have_posts()) : while (have_posts()) : the_post(); ?>

I was wondering if it’s possible to modify this code so that it displays the post via category and then alphabetically ?

The reason being is that each category uses a different coloured link so it looks smarter grouping the posts from a each category.

Any help welcome, cheers