Nice use of colors and clusters; shows that a minimal amount of pixels, carefully chosen, can evoke a place and a feeling.  Only one of them seems a little more rough-and-ready than the rest: the 3rd row, far right image (forest in the mist), which could probably be "fixed" quickly by tweaking the two closest trees.  (But of course these are, according to the description, practice pieces...and as such they're certainly better than any of my own.)