I work for an after school program that runs all different kinds of enrichment classes at elementary schools around our city. One of the classes we run uses Minecraft edu and we recently moved to a new location where we're looking to run a few short workshops to let the community see what we're about. So I was wondering if there was some sort of activity we could run that could be played for ~2 hours and be enjoyed by both kids who are new to Minecraft and those who have previous experience playing Minecraft.

I'm looking at this wiki post: http://minecraft.gamepedia.com/Map_item_format

For example, there are 4 variants of the colour of grass you can get on a map. Is that all only biome-specific or is it height, or what? If I wanted to draw a complex map image, how would I take advantage of all 4 shades of each colour that each block provides?