The gravity forms spinner for ajax submit has a class associated with it: ‘gform_ajax_spinner’ for use in styling. This information is surprisingly hard to find on the googles. If you want to change the spinner image entirely, throw this filter in your functions:
add_filter( 'gform_ajax_spinner_url', 'aceify_custom_gforms_spinner' ); function aceify_custom_gforms_spinner( $src ) { return get_stylesheet_directory_uri() . '/img/loading.gif'; }
(obviously change the return value to whatever your spinner image location is)