snow certainly is a tricky one to draw and color... For the most part snow has a shiny surface and is normally mounded like mud so taking a similar approach to drawing mounds of dirt would be a good start. Coloring mounds would also be similar, but instead of dirt like colors you would use a range of cool and warm colors, based on the background of choice. A default is a pale blue to blue grey scheme If it is just a little snow then it gets a bit tougher, Finding the right brush or tool set is key to that, and the color scheme would be similar, just also it would depend on where the snow is. Example being snow on the side of the road would be much dirtier than snow laying on a tree branch so you would have to take that into account as well.
I would recommend looking up some tutorials here on DA for more information on it
Thanks! with drawing snow I usually use the collection of blues and greys, but I never thought of starting with other mounds.. hm. Would you know if it is possible to get other brushes for SAI? All I've seen are ones for photoshop.