Custom Texture Color Bleeding

[fraxanofnexus]

I have created custom DDS textures using Gimp to test yellow lines marking on a road. Everything works ok, apart from the fact that the color on the yellow lines bleeds out in a blocky way into the rest of the road

for some reason. Please see attached file for reference.

 

I saved the Diffuse Texture as DXT1 (No Alpha) and the Normal Map as DXT5, and generated mipmaps on both.

 

Whatever I do, with various compression formats, it doesn't seem to affect anything. Please help!