Fix horizon-fog-belnd where sky is not set.

CHANGELOG.md

@@ -9,6 +9,7 @@
 
 - Heatmap Fix for 3D terrain ([#4571](https://github.com/maplibre/maplibre-gl-js/pull/4571))
 - Fix Map#off to not remove listener with layer(s) registered with Map#once ([#4592](https://github.com/maplibre/maplibre-gl-js/pull/4592))
+- Fix the color near the horizon when terrain is enabled without any sky ([#4607](https://github.com/maplibre/maplibre-gl-js/pull/4607))
 - _...Add new stuff here..._
 
 ## 4.6.0

src/style/sky.ts

@@ -66,6 +66,7 @@ export class Sky extends Evented {
                 'sky-color': 'transparent',
                 'horizon-color': 'transparent',
                 'fog-color': 'transparent',
+                'fog-ground-blend': 1
             };
         }
 

test/integration/render/tests/terrain/fog-no-sky-blend/style.json

@@ -0,0 +1,46 @@
+{
+    "version": 8,
+    "sprite": "local://sprites/sprite",
+    "glyphs": "local://glyphs/{fontstack}/{range}.pbf",
+    "timeout": 60000,
+    "metadata": {
+        "test": {
+            "height": 512,
+            "width": 512,
+            "maxPitch": 85,
+            "operations": [
+                ["wait"]
+            ]
+        }
+    },
+    "center": [
+        35.38,
+        31.55
+    ],
+    "zoom": 15,
+    "pitch": 85,
+    "sources": {
+        "terrain": {
+            "type": "raster-dem",
+            "tiles": [
+                "local://tiles/zero-elevation-terrain-tile.png"
+            ],
+            "minzoom": 7,
+            "maxzoom": 12,
+            "tileSize": 256
+        }
+    },
+    "layers": [
+        {
+          "id": "background",
+          "type": "background",
+          "paint": {
+            "background-color": "red"
+          }
+        }
+    ],
+    "terrain": {
+        "source": "terrain",
+        "exaggeration": 1
+    }
+}