Here is what is in the settings.php
# Mike Challis' Theme Switch configuration
$SITE['allowThemeSwitch'] = false; // set to false to disable the the use of Theme Switcher
$SITE['CSSscreenDefault'] = 'weather-screen-pastel.css';
$SITE['CSSwideOrNarrowDefault'] = 'narrow'; // 'narrow' or 'wide'
Posting a link to your site is always helpful.
What is the following line in Settings.php set to:
$SITE['CSSscreenDefault'] = 'weather-screen-blue.css';