Rather than focusing on the overall "darkness", instead think about hues and contrast. Perhaps cool greens and blues might work better for your intended mood? And darker darks with lighter highlights can help convey the feeling of a jungle. Of course, you'll need to actually draw some jungle tiles too - grass tiles don't communicate "jungle" at all.
sorry for the background, actually the game theme is kinda lonely,depressed character roaming through a jungle, then is the tileset ok or should I make it more darker ?
The colours feel rather dull, and feel like they weren't chosen with any particular mood in mind. The fluffy cloud suggests that this should be a cheery and perhaps cute game, but the ground and grass colours suggest a rainy day.
Unless running on the ceilings and walls is a standard mechanic in this game, consider using different tiles for those from the floors.
ok, thank you very much