fix(patterns): correct non-blocking timing and blink off phase

Co-authored-by: Cursor <cursoragent@cursor.com>

src/patterns/comet_dual.py

@@ -17,8 +17,9 @@ class CometDual:
             d = max(1, int(preset.d))
             now = utime.ticks_ms()
             if utime.ticks_diff(now, last) >= d:
+                bg_color = self.driver.apply_brightness(colors[-1], preset.b)
                 for i in range(self.driver.num_leds):
-                    self.driver.n[i] = (0, 0, 0)
+                    self.driver.n[i] = bg_color
                 c1 = self.driver.apply_brightness(colors[0 % len(colors)], preset.b)
                 c2 = self.driver.apply_brightness(colors[1 % len(colors)] if len(colors) > 1 else colors[0], preset.b)
                 for t in range(tail):