don't override terminal foreground color for pygments themes

Styles without a color should not hardcode to black, and instead use
None, which instructs Pygments to use the terminal's configured
foreground color.

rich/syntax.py

@@ -162,7 +162,7 @@ def get_style_for_token(self, token_type: TokenType) -> Style:
                 color = pygments_style["color"]
                 bgcolor = pygments_style["bgcolor"]
                 style = Style(
-                    color="#" + color if color else "#000000",
+                    color="#" + color if color else None,
                     bgcolor="#" + bgcolor if bgcolor else self._background_color,
                     bold=pygments_style["bold"],
                     italic=pygments_style["italic"],