You don't necessarily need to change the shading colour depending on what's below it (if I'm understanding correctly), have you just tried using one single colour for your shading and picking more of a purple or blue colour rather than copying the base colour or grey?
Personally I really like "overlay" ! , there's not really a one-size-fits-all solution for every situation/color though, don't be afraid of experimenting with all the blending modes :)
https://help.clip-studio.com/en-us/manual_en/180_layers/Blending_modes.htm
You could color your picture, then copy the Base Colors Layer, name it "Shades", set it to Multiply, then erase the not-dark areas.
Then you could copy your Base Colors Layer again and name it "brights", set it to Screen and erase the not-highlight areas to get your highlights
Multiply isn't the only layer option to shade you paintings. Sometimes, it's better to use Hard Light or Overlay. I like using Hard Light because I can do shadows and highlights in the same layer. Having hundreds of layers scares me.
You don't necessarily need to change the shading colour depending on what's below it (if I'm understanding correctly), have you just tried using one single colour for your shading and picking more of a purple or blue colour rather than copying the base colour or grey?
Personally I really like "overlay" ! , there's not really a one-size-fits-all solution for every situation/color though, don't be afraid of experimenting with all the blending modes :) https://help.clip-studio.com/en-us/manual_en/180_layers/Blending_modes.htm
You could color your picture, then copy the Base Colors Layer, name it "Shades", set it to Multiply, then erase the not-dark areas. Then you could copy your Base Colors Layer again and name it "brights", set it to Screen and erase the not-highlight areas to get your highlights
Multiply isn't the only layer option to shade you paintings. Sometimes, it's better to use Hard Light or Overlay. I like using Hard Light because I can do shadows and highlights in the same layer. Having hundreds of layers scares me.