Add example that utilizes terminal default colors

examples/terminal_default.rs

@@ -0,0 +1,27 @@
+extern crate cursive;
+
+
+use cursive::Cursive;
+use cursive::theme::{Color, Theme};
+use cursive::views::TextView;
+
+
+fn custom_theme_from_cursive(siv: &Cursive) -> Theme {
+    let mut theme = siv.current_theme().clone();
+    theme.colors.background = Color::Default;
+    theme
+}
+
+fn main() {
+    let mut siv = Cursive::new();
+    let theme = custom_theme_from_cursive(&siv);
+
+    // We can quit by pressing `q`
+    siv.add_global_callback('q', Cursive::quit);
+    siv.set_theme(theme);
+
+    siv.add_layer(TextView::new("Hello World with default terminal background color!\n\
+                                Press q to quit the application."));
+
+    siv.run();
+}