Fix ActivateSubScreen: prevent .turnOn from falling through to clear

The .turnOn path was setting $1D=1 then falling through to .normal
which cleared $1D - immediately undoing the overlay enable.

Fix: Add BRA .exit after setting $1D in .turnOn path.
Also remove the unnecessary module $0E check - the real bug was
the fall-through, not menu state interference.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Overworld/ZSCustomOverworld.asm

@@ -1570,18 +1570,16 @@ ActivateSubScreen:
         .turnOn
         SEP #$20 ; Set A in 8bit mode.
 
-        ; Turn on BG1.
+        ; Turn on BG1 and exit (don't fall through to clear!)
         LDA.b #$01 : STA.b $1D
+        BRA .exit
 
     .normal
-
+    ; No overlay needed - clear $1D
     SEP #$20 ; Set A in 8bit mode.
+    STZ.b $1D
 
-    ; Only clear $1D if not in menu (module $0E)
+    .exit
-    LDA.b $10 : CMP.b #$0E : BEQ .skipClear
-        STZ.b $1D        ; Only clear if no overlay needed AND not in menu
-    .skipClear
-
     PLX
 
     PLB

oracle.org

@@ -84,6 +84,14 @@ This section tracks tasks focused on improving the existing codebase's structure
       - [X] Convert all logic blocks (`RunClock`, `DrawClockToHud`, `ColorSubEffect`) into proper `subroutine`s.
       - [X] Break down the large `RunClock` routine into smaller, single-purpose functions (e.g., `TimeSystem_CheckCanRun`, `TimeSystem_IncrementTime`, `TimeSystem_UpdatePalettes`).
 
+*** TODO [#A] Fix Time System Custom BG Color Regression
+    :PROPERTIES:
+    :ID: bug-time-system-bg-color
+    :END:
+    - *Symptom:* Custom background color not working correctly after recent changes.
+    - *Likely Cause:* Regression introduced during system refactoring or ZSCustomOverworld changes.
+    - *Files to Investigate:* =Overworld/time_system.asm=, =Overworld/ZSCustomOverworld.asm=
+
 ** Minecart System (=Sprites/Objects/minecart.asm=)
 *** TODO [#B] Refactor Minecart System [0/4]
     :PROPERTIES: