These are more like illustrations than pictograms, which should be able to work in just B&W. Think of them as having as little detail as possible to help the viewer read the form. I'd go back to just shape and line to help reduce. That being said, I do think that the illustrations are very clear for representing each of your categories.
Cool cool, I did originally do them in black and white, but I wanted to add some color to each of them to make them more distinct
Yes, they should be simple, graphic and read in black and white before you add color them.
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