Add custom classes to TinyMCE in WordPress because I hate shortcodes :)

add_custom_classes_tinymce_wordpress.php

<?php
/* Add the Style Dropdown Menu to the second row of visual editor buttons
 * N.B. Make sure you include your custom classes in both your style.css AND editor-style.css :)
 */
function pico_themes_mce_buttons( $buttons ) {
	array_unshift( $buttons, 'styleselect' );

	return $buttons;
}

add_filter( 'mce_buttons_2', 'pico_themes_mce_buttons' );

function pico_themes_mce_before_init( $init_array ) {
	// Get the current post type and add in the classes
	$current_post_type = pico_themes_get_current_post_type();

	if ( $current_post_type == 'slider' ) {
		
		$style_formats = array(
			// Each array child is a format with it's own settings
			array(
				'title'   => 'Slider Green',
				'inline'   => 'span',
				'classes' => 'slidergreen',
			),
		);
		// Insert the array, json encoded, into 'style_formats'
		$init_array['style_formats'] = json_encode( $style_formats );
	
		return $init_array;
		
	} else {
		
		$style_formats = array(
			// Each array child is a format with it's own settings
			array(
				'title'   => 'Green Button',
				'inline'   => 'span',
				'classes' => 'reenbutton',
			),
		);
		// Insert the array, json encoded, into 'style_formats'
		$init_array['style_formats'] = json_encode( $style_formats );

		return $init_array;
	}
}

add_filter( 'tiny_mce_before_init', 'pico_themes_mce_before_init' );

/**
 * Gets the current global post type if one is set
 */

function pico_themes_get_current_post_type() {

	global $post, $typenow, $current_screen;

	if ( $post && $post->post_type ) {
		$post_type = $post->post_type;
	} elseif ( $typenow ) {
		$post_type = $typenow;
	} elseif ( $current_screen && $current_screen->post_type ) {
		$post_type = $current_screen->post_type;
	} elseif ( isset( $_REQUEST['post_type'] ) ) {
		$post_type = sanitize_key( $_REQUEST['post_type'] );
	} else {
		$post_type = null;
	}

	return $post_type;
}

You're mixing tabs and spaces...

Also, it's good practice to use braces even when you don't need to. You should probably avoid the long-style syntax for blocks (if/endif) when purely in code, they're mainly for use in templates.

it's good practice to use braces even when you don't need to

I agree for the multi-line blocks (where endif; is used). For one liners, it's fine and meets the WordPress coding standards. I'm not sure if you were referring to this one, too, but since you said "even when you don't need to" I wanted to point it out. For example:

if ( condition() )
    do_it()
else
    do_something_else()