I'm not very good at shading in general, but I find lighter colors harder to shade because I usually use a dark purple on multiply to shade and it looks like overkill on light drawings. If I lighten the opacity of the layer, though, the darker colors don't show up as well so I usually have to make another layer. It's complicated gahhh.
It honestly depends on the character, I think. I find shading fine, and I love making adjustments to my shading style, but I think that one of the worst things about shading is shading pure black or pure white characters, but darker is a slightly more challenging thing to shade, when you have to make adjustments you don't usually make to make the shading work c:
It's weird...its not just dark/light colours, its when I work with greys. I can shade a light character that isn't completely white well, but I can do the same with a dark one (say the light one is light green and the dark is dark blue)
but if they are direct grey, black, or white, I find it really hard since there isn't any colour to work with and its confusing when choosing a shading colour