I don't think you actually mean 'header'. A header is something the website send to your browser, like "Content-Type: text/html; charset=utf-8". In addition, you're just passing variables to a script! It would be far easier to edit your script to include the lines
PHP Code:
if(empty($_GET['size'])) $size='large';
if(empty($_GET['color'])) $color='green';
or similarly in a non-PHP language.
However, if you
have to do it with .htaccess (which as before, I don't recommend - I suspect you're
asking the wrong question) then I believe the following will work:
Code:
RewriteEngine on
RewriteRule ^$ /index.php?size=large&color=green [L]
Hope this helps,