Looking through the DrawRain function, I was unable to find a way to alter the color of the rain. So I searched a bit on the forum:
As for the color of the rain.. it's dependant on your palette.. and the positions of the white/grayscale in that palette. It's not hard coded to any specific colour, but rather chooses levels of grayscale based on the spacial position the rain is to be placed on the screen. ie: the closer the rain to the front of the screen, the lighter the colour will be... and that enhances the 3d effect of the rain...
So, it doesn't seem to be hard coded in anyway. How would one hard code the color of the rain, so that it, for instance, would be possible to rain lava (orange), blood (red) or toxic waste (green)?