Step 1: Make sure your image is a square .png with dimensions of 256x256, 512x512, 1024x1024, 2048x2048, or 4096x4096. Here's what I'll be using for this little guide:
Step 2: Import your image to FurryVNE with the "+" next to the "Local Assets" tree:
Step 4: Under the TextureBuilder > Layers tree for whichever part you're applying the image, create 3 texture layers named thusly. "BaseColor" is just a folder I put them in, so don't worry about that. You may consider doing the same, though.
Step 5: Do the same thing in the appropriate "Masks" tree, as well, creating 3 "Texture" masks and naming them as above.
Step 6: For BaseColorR, change the settings to match mine. Make a new color that is 100% red (255, 0, 0) and change the albedo blend mode to "Difference". Assign the "BaseMaskR" texture mask that you made to it, too. Make sure Emission, Metalness, and Smoothness opacities are all zero!
Step 7: Do the same for the remaining 2 texture layers, making sure the "BaseColorG" layer is 100% green (0,255,0) and the "BaseColorB" layer is 100% blue (0,0,255) and both use "Difference" for their albedo blend mode.
Step 8: Now you just need to assign the appropriate color channels to the corresponding texture masks you made. For "BaseMaskR", assign the R channel from your imported image when selecting its texture. Do the same for green and blue, and suddenly:
Use this to assign texture maps you made in external programs, like Substance Painter, Mudbox, or Photoshop!