The color is much better. Might be a little too gray, though that could be the battlefield. Post rain animations/videos of this map as it is now, and brighter. If that doesn't look right, then increase the blue or decrease the non-blue colors (make it less gray) by 10%.
The fog needs work - check out videos of Tenchu and Tenchu 2 on youtube, specifically levels where it rains, and levels with fog and smoke. Vagrant story might also have something to contribute, but I don't remember if it ever rains (maybe during the prologue?), though it is foggy in places. The Snowfly Forest might help.
Fog sticks to the lowest lying areas available, near water, near areas that don't get as much sunlight as nearby areas, and places that fit all the previous criteria and are also shielded from the wind.
There are many different types of rain, but rainfall usually follows a pattern.
*It gets dark.
*isolated drops fall, usually round and fat.
*More drops fall, faster and faster.
*Eventually, you get the "sheet" of rain, where rain falls evenly over all the ground, and is moved in sheets by the wind. You get some turbulance around areas where the wind is blocked or channeled into weird shapes.
But all this isn't needed. All we need is for someone to find and reverse-engineer both the raind drops and the rain landing animations, and then you implement something similiar. You can get away with a cheap effects if you vary the tempo and drop distribution from among several patterns, chosen at random.
It'll help if you post gifs or videos. Youtube is fine.