https://civitai.com/models/466467/skin-color-slider --- this slider has been working excellent for me, you can also fine tune it pretty well to your desired skin tone. Helpful for checkpoints where getting images of black people is difficult. This slider also have minimal effect on generation unless you use high or low weights, but I found -0.3 to 1 to be sufficient for most use cases. Works with SDXL as well, but needs higher weights.