Solution:
You can do this by using the “value” property of the parameter array(s) for vc_map() or vc_add_parameter(). Documentation is here… see the description of the value property.
An example would be:
function vc_myshortcode(){
vc_map({
'name' => 'My Shortcode',
'base' => "myshortcode",
'params' => array(
array(
'type'=>'textfield',
'holder'=>'div',
'param_name'=>'color',
'value'=>'#333333'
)
)
})}
add_action( 'vc_before_init', 'vc_myshortcode' );
So the default value for the color parameter would then be set to #333333