Pokemon's much lower-contrast than your tiles in all cases where the character overlaps those tiles (they can do whatever they want with the trees since the player doesn't overlap those). For example, compare their grass tiles and path tiles.  They're quite similar in value. Compare the grass and paths in yours. They contrast a lot.

I recommend juxtaposing your tiles with Pokemon G/S/C on the same canvas if you don't see what I mean. It might help you! Even just comparing the values, Pokemon's range of values is much narrower than yours. Notice how even on the trees, which he player doesn't overlap, the darkest colours are nowhere near as dark as your dark colours. Pokemon looks quite pale in comparison :]

Your actual pixel work's fine, the colours could just use changes to reduce the contrast.

Hmm, I would usually agree with you, but for this I'm trying for a pokemon esque style, because I enjoy the high contrast for that type of game.

I'm sure you know what Pokemon Silver looks like, but just in case...
http://i81.servimg.com/u/f81/11/31/64/75/gold_219.png

For an environment tileset, the contrast is very high. Character sprites will be quite difficult to see on top of this. High contrast is good for sprites and illustrations, but environments/backgrounds should generally have lower contrast so that they "recede" and don't clash with the foreground/sprites.