根据@ aaronsti的回答，我发现以下内容对我有用。将拇指图像设置为 nil 无效。

On basis of @aaronsti's answer I found that the following worked for me. Setting thumb-image to nil had no effect.

  [_slider setThumbImage:[_slider thumbImageForState:UIControlStateNormal] forState:UIControlStateNormal];
_slider.minimumTrackTintColor = minTintColor;
_slider.thumbTintColor = thumbTintColor;