ParticleRender startColor in Gradient / Two-Gradient Mode doesn't take effect

[JujieX]

Describe the bug ParticleRender startColor in Gradient Mode doesn't take effect

To Reproduce

  main.startColor.mode = ParticleGradientMode.Gradient;
  const gradient = main.startColor.gradient;
  gradient.addColorKey(0, new Color(1, 0, 0, 1));
  gradient.addColorKey(1, new Color(1, 0, 0, 1));
  gradient.addAlphaKey(0, 1);
  gradient.addAlphaKey(1, 1);