Okay, I decided that my previous tutorial for 6 colored masks, while extremely effective following my terrain tutorial, is completely useless on other programs and for people who don't work with layers. Also, some of you already have your terrain done the way you like to make them, which means they are one layer. This tutorial, while not as pretty as my other one, is for you.
I am making this assuming you already know how to do a simple 3 color mask.
Step 1: Load up your terrain. You'll want this for a reference. Put it in RGB mode.
Step 2: Begin making your mask using Red, Green, Blue, and three other colors. Save as a .PNG called "mapnameMaskWIP"
Step 3: Fill in all the colors except for Red, Green and Blue with black. Save as a .PNG called "MapnameMask"
Step 4: Reload "MapnameMaskWIP.png". This time fill in Red, Green, and Blue with black. Change the other three colors into Red Green and Blue. Save it as a .PNG named "Mapnamemask2"
Step 5: Run the mapmaker. Enter the terrain and "mapnamemask.png". Keep pressing the right arrow where the terrain textures are until the mask option becomes blank. Enter " MapnameMask2.png" here.
Congrats! You should be able to use 6 terrain masks with no problem