Unable to pass list of stroke_color for opengl

Nobody has claimed this yet.

## Description of bug / unexpected behavior

It used to be the case you could pass a list of colors to create a stroke gradient, but from what I can tell it was broken from #2332 as I get the error `AttributeError: 'list' object has no attribute 'startswith'`

## Expected behavior

Passing a list of `stroke_color` creates a gradient

## How to reproduce the issue

Run the below scene with the opengl renderer

Code for reproducing the problem

```py
class Sample(Scene):

def construct(self):
self.add(Rectangle(stroke_color=[BLUE, GREEN]))
```

## Additional media files

Images/GIFs

## Logs
Terminal output

```
/home/k4pran/.cache/pypoetry/virtualenvs/manim-HpVtdmRp-py3.10/bin/python -m manim /home/k4pran/PycharmProjects/manim/sample.py --renderer opengl -pql
Manim Community v0.16.0.post0

╭───────────────────── Traceback (most recent call last) ──────────────────────╮
│ /home/k4pran/PycharmProjects/manim/manim/cli/render/commands.py:110 in │
│ render │
│ │
│ 107 │ │ │ while keep_running: │
│ 108 │ │ │ │ for SceneClass in scene_classes_from_file(file): │
│ 109 │ │ │ │ │ scene = SceneClass(renderer) │
│ ❱ 110 │ │ │ │ │ rerun = scene.render() │
│ 111 │ │ │ │ │ if rerun or config["write_all"]: │
│ 112 │ │ │ │ │ │ renderer.num_plays = 0 │
│ 113 │ │ │ │ │ │ continue │
│ │
│ /home/k4pran/PycharmProjects/manim/manim/scene/scene.py:221 in render │
│ │
│ 218 │ │ """ │
│ 219 │ │ self.setup() │
│ 220 │ │ try: │
│ ❱ 221 │ │ │ self.construct() │
│ 222 │ │ except EndSceneEarlyException: │
│ 223 │ │ │ pass │
│ 224 │ │ except RerunSceneException as e: │
│ │
│ /home/k4pran/PycharmProjects/manim/sample.py:9 in construct │
│ │
│ 6 │ def construct(self): │
│ 7 │ │ # self.add(Arc(angle=TAU, stroke_color=[PURE_BLUE, PURE_RED])) │
│ 8 │ │ # self.wait(duration=10) │
│ ❱ 9 │ │ self.add(Rectangle(stroke_color=[BLUE, GREEN])) │
│ │
│ /home/k4pran/PycharmProjects/manim/manim/mobject/geometry.py:2472 in │
│ __init__ │
│ │
│ 2469 │ │ close_new_points=True, │
│ 2470 │ │ **kwargs, │
│ 2471 │ ): │
│ ❱ 2472 │ │ super().__init__(UR, UL, DL, DR, color=color, **kwargs) │
│ 2473 │ │ self.stretch_to_fit_width(width) │
│ 2474 │ │ self.stretch_to_fit_height(height) │
│ 2475 │ │ v = self.get_vertices() │
│ │
│ /home/k4pran/PycharmProjects/manim/manim/mobject/geometry.py:1930 in │
│ __init__ │
│ │
│ 1927 │ """ │
│ 1928 │ │
│ 1929 │ def __init__(self, *vertices: Sequence[float], **kwargs): │
│ ❱ 1930 │ │ super().__init__(vertices, **kwargs) │
│ 1931 │
│ 1932 │
│ 1933 class RegularPolygram(Polygram): │
│ │
│ /home/k4pran/PycharmProjects/manim/manim/mobject/geometry.py:1751 in │
│ __init__ │
│ │
│ 1748 │ """ │
│ 1749 │ │
│ 1750 │ def __init__(self, *vertex_groups: Iterable[Sequence[float]], col │
│ ❱ 1751 │ │ super().__init__(color=color, **kwargs) │
│ 1752 │ │ │
│ 1753 │ │ for vertices in vertex_groups: │
│ 1754 │ │ │ first_vertex, *vertices = vertices │
│ │
│ /home/k4pran/PycharmProjects/manim/manim/mobject/types/opengl_vectorized_mob │
│ ject.py:133 in __init__ │
│ │
│ 130 │ │ if fill_color: │
│ 131 │ │ │ self.fill_color = Color(fill_color) │
│ 132 │ │ if stroke_color: │
│ ❱ 133 │ │ │ self.stroke_color = Color(stroke_color) │
│ 134 │ │
│ 135 │ def get_group_class(self): │
│ 136 │ │ return OpenGLVGroup │
│ │
│ /home/k4pran/.cache/pypoetry/virtualenvs/manim-HpVtdmRp-py3.10/lib/python3.1 │
│ 0/site-packages/colour.py:988 in __init__ │
│ │
│ 985 │ │ if isinstance(color, Color): │
│ 986 │ │ │ self.web = color.web │
│ 987 │ │ else: │
│ ❱ 988 │ │ │ self.web = color if color else 'black' │
│ 989 │ │ │
│ 990 │ │ self.equality = RGB_equivalence │
│ 991 │
│ │
│ /home/k4pran/.cache/pypoetry/virtualenvs/manim-HpVtdmRp-py3.10/lib/python3.1 │
│ 0/site-packages/colour.py:1006 in __setattr__ │
│ │
│ 1003 │ def __setattr__(self, label, value): │
│ 1004 │ │ if label not in ["_hsl", "equality"]: │
│ 1005 │ │ │ fc = getattr(self, 'set_' + label) │
│ ❱ 1006 │ │ │ fc(value) │
│ 1007 │ │ else: │
│ 1008 │ │ │ self.__dict__[label] = value │
│ 1009 │
│ │
│ /home/k4pran/.cache/pypoetry/virtualenvs/manim-HpVtdmRp-py3.10/lib/python3.1 │
│ 0/site-packages/colour.py:1084 in set_web │
│ │
│ 1081 │ set_hex_l = set_hex │
│ 1082 │ │
│ 1083 │ def set_web(self, value): │
│ ❱ 1084 │ │ self.hex = web2hex(value) │
│ 1085 │ │
│ 1086 │ ## range of color generation │
│ 1087 │
│ │
│ /home/k4pran/.cache/pypoetry/virtualenvs/manim-HpVtdmRp-py3.10/lib/python3.1 │
│ 0/site-packages/colour.py:664 in web2hex │
│ │
│ 661 │ │
│ 662 │ │
│ 663 │ """ │
│ ❱ 664 │ if web.startswith('#'): │
│ 665 │ │ if (LONG_HEX_COLOR.match(web) or │
│ 666 │ │ │ (not force_long and SHORT_HEX_COLOR.match(web))): │
│ 667 │ │ │ return web.lower() │
╰──────────────────────────────────────────────────────────────────────────────╯
AttributeError: 'list' object has no attribute 'startswith'

Process finished with exit code 1

```

## System specifications

System Details

- OS (with version, e.g., Windows 10 v2004 or macOS 10.15 (Catalina)):
- RAM:
- Python version (`python/py/python3 --version`):
- Installed modules (provide output from `pip list`):
```
PASTE HERE
```

LaTeX details

+ LaTeX distribution (e.g. TeX Live 2020):
+ Installed LaTeX packages:

FFMPEG

Output of `ffmpeg -version`:

```
PASTE HERE
```

## Additional comments

Start with manim/mobject/types/opengl_vectorized_mobject.py at the OpenGL mobject initialization shown in the traceback, then reproduce the issue with Rectangle(stroke_color=[BLUE, GREEN]) using the OpenGL renderer. Done means the scene renders successfully and a list of stroke colors produces the expected gradient without the AttributeError.

Written by the indexing model from the issue text.