Yo welcome back! For color studies I think these are fine, the only point that stands out is that though the palettes are fine and colors complement each other, there's not much distinction on the side of saturation or hue. Just like line weight draws the eye around the drawing and makes things easier to distinguish, so do values, tones and saturation for color. I personally do find these harder to manage, I don't remember how in depth Marc went over it.
Some of the exercices will ask to copy palettes from other artists, try to keep an eye not only for the color tone, but for some of the other values as well and how they affect your perception of the piece.