Value is used to create the illusion of depth. Space can be 2D, 3D, negative and/or positive. Because value creates contrast/texture and makes it look like it has depth. Space can do many things; add more space between lines and it looks more 3D, add less and it looks 2D in some drawings or the opposite in other drawings
I don't think it would be considered plagiarism if you make it yourself but to just to be sure, you should maybe switch a few colors up and credit the author just to be on the safe side.