Terrain Shader with Organtic Texture

[ZuluTangoDelta]

Hi i am trying to create a painttool for terrains.I try it with blendmaps so if there is a green pixel on the blendmap then texture A apears on the terrain,if there is a orange pixels on the blendmap texture b apears on the terrain....The problem are the edges of the textures.So with this methode it only works with three textures (R,G,B) and if i want mor textures it doesnt work My source:

http://www.google.de/imgres?imgurl=http%3A%2F%2Fallenwp.com%2Fblog%2Fwp-content%2Fuploads%2F2010%2F05%2FToyFactory_Multi-texturing_organic.jpg&imgrefurl=http%3A%2F%2Fallenwp.com%2Fblog%2F2010%2F05%2F06%2Fsimple-fast-gpu-driven-multi-textured-terrain%2F&h=576&w=768&tbnid=kktZp3kbZQjW_M%3A&zoom=1&docid=ETKkK_XkHVJcrM&ei=dPFOU9qfIsb-ygOw2ILgAQ&tbm=isch&iact=rc&uact=3&dur=221&page=1&start=0&ndsp=10&ved=0CFgQrQMwAA