Wordpress and use conditional arrays

I use simple form for send values for search inside query for wordpress , but in some cases from this simple form no all values need search , in some cases one value or 3 values , etc , i use this for the search , this search based in attributes

$args = array
( 
'post_type'             => 'product',
'post_status'           => 'publish',
'ignore_sticky_posts'   => 1,
'orderby'               => $orderby,
'order'                 => $order,
'posts_per_page'        => $per_page,



'meta_query'=> array
(
array
(
'key'           => '_visibility',
'value'         => array('catalog', 'visible'),
'compare'       => 'IN'
)
),


'tax_query' => array
(
///
array
(
'taxonomy'      => 'pa_' . $attribute,
'terms'         => explode(",",$values),
'field'         => 'slug',
'operator'      => 'IN'
),

array
(
'taxonomy'      => 'pa_colors',
'terms'         => explode(",","Verdes"),
'field'         => 'slug',
'operator'      => 'IN'
),
///
)


);

The case it´s i need search in many moments more of 1 value , and for each new value i need put other array inside function , for example :

 array
   (
    'taxonomy'      => 'pa_colors',
     'terms'        => explode(",","Green"),
    'field'         => 'slug',
     'operator'         => 'IN'
     ),

    )

By this my question is if it´s possible put conditional ( as if , etc ) for each array , i know no right this syntax i writte now , but for understand my idea :

if(isset($_POST['colors']))
{
   array
       (
        'taxonomy'      => 'pa_colors',
         'terms'        => explode(",","Green"),
        'field'         => 'slug',
         'operator'         => 'IN'
         ),

        )
}

That´s my question , how i can do this , thank´s help me , and regards

via Chebli Mohamed