Hello, I hope all is well!

I am working on a technical illustratoration of my model and I wanted to change the line color for certain parts. Every time I try and save it as a vector file or preview the file, all the lines show up black in color. I'm pretty sure my settings are off somewhere, but would any know how I would go about saving my vector image with some parts grey and some parts black? I have attached an image of my model of how I would like it to look.

If anyone can help that would be great, thank you!