ACF no print data [closed]

I assume you want the field for the current category archive, not the category of the post inside the loop? Try get_queried_object_id() instead of the_category_ID( $echo ).

In single.php, you just need a slightly different iteration of your original attempt:

if ( $terms = get_the_category() )
    the_field( 'bgcolor', 'category_' . $terms[0]->term_id );