I don't think it's your machine, although I hadn't tested this until now because I almost never use shuffle. :)

I think the problem is that they're indicating state by toggling between your chosen accent color and black. If your accent color is, say, pink, the difference is pretty obvious, but if your accent color is relatively dark, like blue or purple, it's harder to see. It seems like they could solve this by toggling between the accent color and gray, or "lighting up" a solid roundrect of the accent color around the control when it's on.