You have to be braver with the contrast..
Try squinting your eyes, you should still be able to see some of the strong highlights giving shape to the tank..
Or if you look at it from far away, you should still be able to see the important sprites in the game. If it all blends together, you'll have big issues with readability of the game, even if you play the game really zoomed in, it's better with really clear and defined shapes and shading.
Look at and compare with other pixel art games.
