First attempt at converting $color themes to CSS stylesheets. Seems to work pretty well. This will need to be modified as CSS is cleaned up.

themes/color_theme_to_css.php

@@ -0,0 +1,362 @@
+#!/usr/bin/env php
+<?php
+/**
+ * color_theme_to_css.php
+ *
+ * This script can be used to convert an old $color theme to a stylesheet for
+ * use with templates.  Output is sent to STDOUT.
+ * 
+ * HOWTO:
+ *      1. Create a .php file containing your $color theme.
+ *      2. Run this script from a command line, giving the name of your theme file
+ *         as an arguement to this script, e.g.:
+ *
+ *            /path/to/squirrelmail/templates/theme_to_css.php /path/to/mytheme.php
+ * 
+ *         To send the output to a .css file, do the following:
+ *
+ *            /path/to/squirrelmail/templates/theme_to_css.php /path/to/mytheme.php > my_theme.css
+ *
+ * @copyright &copy; 1999-2006 The SquirrelMail Project Team
+ * @license http://opensource.org/licenses/gpl-license.php GNU Public License
+ * @version $Id$
+ * @package squirrelmail
+ * @subpackage templates
+ * @author Steve Brown
+ * @since 1.5.2
+ */
+
+if (empty($argv[1])) {
+    echo "Please provide the path to the file containing the \$color theme you\n" .
+         "wish to convert to a stylesheet.\n\n";
+    exit (1);
+}
+
+$theme_file = $argv[1];
+if (!is_file($theme_file) || !is_readable($theme_file)) {
+    echo "The requested theme could not be converted because the file could not\n" .
+         "be opened.  Please specify a theme file that can be read.\n\n";
+    exit(1);
+}
+
+/* set default colors in case color theme is not full */
+$def_color = array();
+$def_color[0]   = '#dcdcdc'; // (light gray)     TitleBar
+$def_color[1]   = '#800000'; // (red)
+$def_color[2]   = '#cc0000'; // (light red)      Warning/Error Messages
+$def_color[3]   = '#a0b8c8'; // (green-blue)     Left Bar Background
+$def_color[4]   = '#ffffff'; // (white)          Normal Background
+$def_color[5]   = '#ffffcc'; // (light yellow)   Table Headers
+$def_color[6]   = '#000000'; // (black)          Text on left bar
+$def_color[7]   = '#0000cc'; // (blue)           Links
+$def_color[8]   = '#000000'; // (black)          Normal text
+$def_color[9]   = '#ababab'; // (mid-gray)       Darker version of #0
+$def_color[10]  = '#666666'; // (dark gray)      Darker version of #9
+$def_color[11]  = '#770000'; // (dark red)       Special Folders color
+$def_color[12]  = '#ededed'; // (light gray)     Alternate color for message list
+$def_color[13]  = '#800000'; // (dark red)       Color for quoted text -- > 1 quote
+$def_color[14]  = '#ff0000'; // (red)            Color for quoted text -- >> 2 or more
+$def_color[15]  = '#002266'; // (dark blue)      Unselectable folders
+$def_color[16]  = '#ff9933'; // (orange)         Highlight color
+
+$color = $def_color;
+include($theme_file);
+if ($color === $def_color) {
+    echo "The theme file you specified did not make any alterations to the default\n" .
+         "color scheme.  Please choose a different file.\n\n";
+    exit(1);
+}
+
+$css_source = <<<CSS
+/* older css template */
+/* page body formatting */
+body {
+    color:  __COLOR8__;
+    background-color: __COLOR4__;
+}
+body.sqm_leftMain {
+    color:  __COLOR6__;
+    background-color: __COLOR3__;
+}
+
+/* right links */
+a:link, a:visited, a:hover, a:active {
+    color: __COLOR7__;
+}
+
+/* left links */
+.sqm_leftMain a:link, .sqm_leftMain a:visited, .sqm_leftMain a:hover, .sqm_leftMain a:active {
+    color:  __COLOR6__;
+}
+.leftunseen, .leftspecial, .leftspecial a:link, .leftspecial a:visited, .leftspecial a:hover, .leftspecial a:active {
+    color:  __COLOR11__;
+}
+.leftnoselect a:link, .leftnoselect a:visited, .leftnoselect a:hover, .leftnoselect a:active {
+    color:  __COLOR15__;
+}
+
+/* highlighted texts */
+.highlight {
+    color:  __COLOR15__;
+}
+.error_table {
+    color: __COLOR14__;
+    border: 2px solid __COLOR0__;
+    background-color: __COLOR3__;
+}
+.error_thead {
+    background-color: __COLOR10__;
+}
+.error_thead_caption {
+    background-color: __COLOR10__;
+}
+.error_row {
+    color: __COLOR14__;
+}
+.error_val {
+    color: __COLOR8__;
+    border: 2px solid __COLOR0__;
+
+}
+.error_key {
+    border: 2px solid __COLOR0__;
+    color: __COLOR14__;
+    background-color: __COLOR0__;
+}
+
+/* Standard defs */
+table.table1    {
+    border: 1px solid __COLOR0__;
+}
+table.table2    {
+    border: 1px solid __COLOR9__;
+}
+td.header1  {
+    background: __COLOR0__;
+}
+td.header2  {
+    background: __COLOR9__;
+}
+td.header4  {
+    background: __COLOR5__;
+}
+tr.even {
+    background: __COLOR12__;
+}
+tr.odd  {
+    background: __COLOR4__;
+}
+.table_standard {
+    border:1px solid __COLOR0__;
+}
+
+.sqm_loginOrgName, .sqm_signoutBar {
+    background: __COLOR0__;
+}
+.sqm_motd {
+    background: __COLOR9__;
+}
+.sqm_motd td {
+    background: __COLOR4__;
+}
+
+/* empty_folder.tpl defs */
+.sqm_emptyFolder {
+    background: __COLOR9__;
+}
+.sqm_emptyFolder td {
+    background: __COLOR4__;
+}
+
+/* error_box.tpl definitions */
+.table_errorBoxWrapper   {
+    background: __COLOR9__;
+}
+.table_errorBox  {
+    background: __COLOR0__;
+}
+.error_message {
+    background: __COLOR4__;
+}
+
+/* page_header.tpl definitions */
+.sqm_currentFolder  {
+    background: __COLOR9__;
+}
+.sqm_headerSignout  {
+    background: __COLOR9__;
+}
+
+/* message_list.tpl definitions */
+.table_messageListWrapper   {
+    background: __COLOR9__;
+}
+
+.table_messageList  {
+    background: __COLOR5__;
+}
+.table_messageList td.spacer {
+    background: __COLOR0__;
+}
+.table_messageList  tr.mouse_over   {
+    background: __COLOR5__;
+}
+.table_messageList  tr.clicked  {
+    background: __COLOR16__;
+}
+.deleted    {
+    color: __COLOR9__;
+}
+.flagged    {
+    color: __COLOR2__;
+}
+.high_priority  {
+    color: __COLOR1__;
+}
+.low_priority   {
+    color: __COLOR8__;
+}
+.message_list_controls {
+    background: __COLOR0__;
+}
+.spacer {
+    background: __COLOR4__;
+}
+
+/* folder_manip.tpl defs */
+#folderManip   table.wrapper   {
+    border: 1px solid __COLOR0__;
+}
+#folderManip   td.folderAction {
+    background: __COLOR0__;
+}
+
+/* addressbook_list.tpl defs */
+#addressList    table   {
+    border: 1px solid __COLOR9__;
+}
+#addressList    td.header1  {
+    background: __COLOR9__;
+}
+#addressList    td.abookSwitch  {
+    background: __COLOR0__;
+}
+
+#addressList    td.abookButtons  {
+    background: __COLOR0__;
+}
+#addressList    td.abookField   {
+    border-left: 1px solid __COLOR9__;
+    border-right: 1px solid __COLOR9__;
+}
+#addressList    td.colHeader {
+    background: __COLOR9__;
+}
+#addrBookSearch   table.wrapper   {
+    border: 1px solid __COLOR9__;
+}
+#addrAddEdit    table   {
+    border: 1px solid __COLOR9__;
+}
+#addrAddEdit    td.header   {
+    background: __COLOR9__;
+}
+
+/* options defs */
+#optionGroups   table   {
+    border: 1px solid __COLOR0__;
+}
+#optionGroups   td.title    {
+    background: __COLOR0__;
+}
+#optionGroups   td.optionElement    table   {
+    border:1px solid __COLOR9__;
+}
+#optionGroups   td.optionName   {
+    background: __COLOR9__;
+}
+#optionGroups   td.optionDesc   {
+    background: __COLOR0__;
+}
+#optionDisplay  table   {
+    border: 1px solid __COLOR0__
+}
+#optionOrder    table   {
+    border: 1px solid __COLOR0__
+}
+#optionOrder    table.moveFields    td  {
+    border-left: 1px solid __COLOR0__;
+    border-right: 1px solid __COLOR0__;
+}
+#optionsIdentity    table.table2 tr  {
+    background: __COLOR0__;
+}
+#optionsIdentity hr  {
+    width: 95%;
+    border: 1px solid __COLOR9__;
+}
+
+/* help defs */
+#help   td.nav  {
+    color: __COLOR0__;
+}
+
+/* search defs */
+div.search td.header4  {
+    border-bottom: 1px solid __COLOR9__;
+}
+div.search td.queryAction {
+    border-left: 1px solid __COLOR9__;
+    border-top: 1px solid __COLOR9__;
+    border-bottom: 1px solid __COLOR9__;
+}
+
+div.search td.queryDesc  {
+    border-top: 1px solid __COLOR9__;
+    border-bottom: 1px solid __COLOR9__;
+}
+div.search span.error  {
+    color: __COLOR2__;
+}
+div.search td.searchForm  {
+    border-right: 1px solid __COLOR0__;
+    border-left: 1px solid __COLOR0__;
+}
+div.search td.queryError {
+    color: __COLOR2__;
+}
+div.search h2 {
+    color: __COLOR2__;
+}
+
+/* compse defs */
+div.compose tr.header {
+    background: __COLOR9__;
+}
+div.compose tr.attachment td {
+    background: __COLOR0__;
+    border-top: 1px solid __COLOR9__;
+    border-bottom: 1px solid __COLOR9__;
+}
+
+div.compose table.close {
+    background: __COLOR0__;
+    border:1px solid __COLOR9__;
+}
+CSS;
+
+$p = array();
+for ($k = 0; $k<=16; $k++) {
+    $p[$k] = '__COLOR'.$k.'__';
+    if (!isset($color[$k])) {
+        $color[$k] = $def_color[$k];
+    }
+}
+
+// Just to make sure...
+ksort($p);
+ksort($color);
+$css_source = str_replace($p, $color, $css_source);
+echo $css_source;
+exit(0);
+?>