diff --git a/1.3-Implementation.md b/1.3-Implementation.md
index 7b5cfdc..2ed2720 100644
--- a/1.3-Implementation.md
+++ b/1.3-Implementation.md
@@ -36,7 +36,7 @@ You will need to make changes. Make sure to read about applying `overrides` on [
   * It is recommended that you clear (Ctrl-Shift-Del) everything (except passwords and site preferences) when first enabling (or permanently disabling) this, so orphaned Origin Attribute data is cleared
 - RFP is enabled (section 4500)
    * :eyes: The **main pref** is `4501`
-   * :eyes: The **letterboxing pref** is `4504` and is currently independent of `4501`. FYI: this is the pref that creates white borders around your webpages
+   * :eyes: The **letterboxing pref** is `4504` and is currently independent of `4501`. FYI: this is the pref that creates borders around your webpages: if you want dark borders, use the hidden pref `ui.systemUsesDarkTheme` = `1`
    * As RFP patches land in stable, alternative existing preferences are moved to section 4600 and made inactive
    * :star: non-RFP users may want to enable section 4600
    * :star: RFP users should reset items in 4600 in about:config, as some cause RFP to not behave as you would expect and alter your fingerprint