SettingsTheme: increase switch thumb contrast

for light the contrast was hard to see

Change-Id: Ib84762b3bce89f3167e9d9a0dd70893f4ab1ab5d
diff --git a/overlay/common/frameworks/base/packages/SettingsLib/SettingsTheme/res/values-v31/colors.xml b/overlay/common/frameworks/base/packages/SettingsLib/SettingsTheme/res/values-v31/colors.xml
index 4bcf1d3..a0d7755 100644
--- a/overlay/common/frameworks/base/packages/SettingsLib/SettingsTheme/res/values-v31/colors.xml
+++ b/overlay/common/frameworks/base/packages/SettingsLib/SettingsTheme/res/values-v31/colors.xml
@@ -2,4 +2,6 @@
 
     <color name="settingslib_track_on_color">@color/settingslib_switch_track_on</color>
 
+    <color name="settingslib_thumb_off_color">@android:color/system_neutral2_100</color>
+
 </resources>