Tim, You were right. Using your code I realized it was prepending the outer array. After changing the code to target the inner array like this:
add_filter( 'acf/fields/wysiwyg/toolbars' , 'my_toolbars' );
function my_toolbars( $toolbars ) {
array_unshift( $toolbars['Basic' ][1], 'forecolor' );
return $toolbars;
}
The Font Color appeared in the Basic Toolbar.
So that seemed to work! Thank you Tim! Your code was spot on and helped me realize there was another nested array.