Hi marcofree !
You open index.php file in templates/ja_koniga folder :
find code section at about line 22 to 31 :
#support extra color themes
$ja_color_themes = array('default','laputa','sakura'); // You can add more color array if needed
$ja_header_images_wide = array ('header1.jpg','header2.jpg','header3.jpg','header4.jpg','header5.jpg');
$ja_header_images_narrow = array ('header1-n.jpg','header2-n.jpg','header3-n.jpg','header4-n.jpg','header5-n.jpg');
####################################
# Change the width of the template
$ja_width_default = 'narrow'; // 'narrow': 800x600; 'wide': 1024x768
# default color
$ja_color_default = 'default'; //blank for default, else pick one of in extra color themes $ja_color_themes
there are 3 color you can select for $ja_color_default (default’,’laputa’,’sakura)
goodluck !