wpdonate_3.php

<?php
if( ! current_user_can( 'manage_options' ) ) {
	exit();
}

$settings_color = "#fff";

if( isset( $_POST['settings_color'] ) && wp_verify_nonce( $_POST['_wpnonce'] ) ) {
	update_option( "myplugin_settings_color", $_POST['settings_color'] );
	if( isset( $_POST['feature_on'] ) ) {
		update_option( "my_plugin_featureon", true );
	} else {
		update_option( "my_plugin_featureon", false );
	}
	echo "<p><strong>Settings Saved!</strong></p>";
}

if( get_option( "myplugin_settings_color" ) !== false  ) {
	$settings_color = get_option( "myplugin_settings_color" );
}

?>
<div class="wrap">
	<h2>Plugin Settings</h2>
	<form action="" method="post">
		<?php wp_nonce_field(); ?>
		<p><input name="feature_on" type="checkbox"  <?php
			if ( get_option( "myplugin_feature_on" ) !== false && get_option( "myplugin_feature_on" ) ) {
				echo 'checked="checked" ';
			}
			?> /> Turn Feature On</p>
		<p>Color: <input type="text" name="settings_color" value="<?php echo $settings_color; ?>" /></p>
		<p><button type="submit">Save Settings</button></p>
	</form>
</div>