Great questions!
On black as a color: It could be considered a gray area (color pun intended), but for the jam I'd say count it as a color. It's in line with say the old school CGA color palettes from games of yesteryear:
On shades as different colors: I'd say yes - dark blue and light blue are different colors going by their hex values. But you might consider dithering to make lighter / darker shades. E.g. https://www.retronator.com/post/176876250028/the-many-shades-of-cga-a-dithering-... shows a 4-color CGA palette that looks like more than 4 colors...
