When you say 'shade', I am guessing that you mean a lighter application of color, rather than blending one color into another? If you mean lighter application, I would suggest watering down the colored ink as you would water down black to make greywash

I find that my color packer acts very much like a shading machine, with very minimal ink insertion on a first pass, and needs going over the area a few times to get the proper saturation, but because the machine hits so softly, it doesn't chew the skin up in the process

If you mean you are trying to blend colors, then I would suggest in addition to the fully colored area in the dark ink, do an area a few mm around it at say 50% saturation, then when you use the next color, over lap that color over the 50% area, so the two colors mix in the skin, before then going on to the area of full color. Kind of hard to describe what I'm meaning... For example
2 cm circle of solid red ink
Then have a 5mm ring of 50% red ink (not watered down pigment, but only one or two passes so the area is not fully saturated)
Then have a 15mm ring of yellow ink, starting at the edge of the 2cm circle. That will then make the 5mm ring of red ink become a 5mm ring of orange ink and create a 1cm ring of yellow ink outside of the 'mixed' area.
Hope that's of help
