diff --git a/src/textual_webterm/svg_exporter.py b/src/textual_webterm/svg_exporter.py
index 4ad85e9..ed4d85b 100644
--- a/src/textual_webterm/svg_exporter.py
+++ b/src/textual_webterm/svg_exporter.py
@@ -68,10 +68,15 @@ def _color_to_hex(color: str, is_foreground: bool = True) -> str:
     if color == "default":
         return DEFAULT_FG if is_foreground else DEFAULT_BG
 
-    # Already a hex color
+    # Already a hex color with #
     if color.startswith("#"):
         return color
 
+    # Hex color without # prefix (pyte's 256-color/truecolor format)
+    # Check if it looks like a hex color (6 hex digits)
+    if len(color) == 6 and all(c in "0123456789abcdefABCDEF" for c in color):
+        return f"#{color}"
+
     # Named color lookup (case-insensitive)
     lower = color.lower()
     if lower in ANSI_COLORS:
diff --git a/tests/test_svg_exporter.py b/tests/test_svg_exporter.py
index 101c623..8430740 100644
--- a/tests/test_svg_exporter.py
+++ b/tests/test_svg_exporter.py
@@ -31,6 +31,13 @@ class TestColorToHex:
         assert _color_to_hex("#123456") == "#123456"
         assert _color_to_hex("#AABBCC") == "#AABBCC"
 
+    def test_hex_color_without_hash(self) -> None:
+        """Hex colors without # prefix (pyte's 256-color/truecolor) get # added."""
+        assert _color_to_hex("ff0000") == "#ff0000"
+        assert _color_to_hex("123456") == "#123456"
+        assert _color_to_hex("AABBCC") == "#AABBCC"
+        assert _color_to_hex("ff8700") == "#ff8700"  # Common 256-color orange
+
     def test_named_colors(self) -> None:
         """Named ANSI colors map correctly."""
         assert _color_to_hex("red") == ANSI_COLORS["red"]