Add example to show auto selection of text color.

docs/examples/styles/color_auto.css

@@ -0,0 +1,26 @@
+Label {
+    color: auto 80%;
+    content-align: center middle;
+    height: 1fr;
+    width: 100%;
+}
+
+#lbl1 {
+    background: red 80%;
+}
+
+#lbl2 {
+    background: yellow 80%;
+}
+
+#lbl3 {
+    background: blue 80%;
+}
+
+#lbl4 {
+    background: pink 80%;
+}
+
+#lbl5 {
+    background: green 80%;
+}

docs/examples/styles/color_auto.py

@@ -0,0 +1,14 @@
+from textual.app import App
+from textual.widgets import Label
+
+
+class ColorApp(App):
+    def compose(self):
+        yield Label("The quick brown fox jumps over the lazy dog!", id="lbl1")
+        yield Label("The quick brown fox jumps over the lazy dog!", id="lbl2")
+        yield Label("The quick brown fox jumps over the lazy dog!", id="lbl3")
+        yield Label("The quick brown fox jumps over the lazy dog!", id="lbl4")
+        yield Label("The quick brown fox jumps over the lazy dog!", id="lbl5")
+
+
+app = ColorApp(css_path="color_auto.css")