The basing was achieved using coarse pumice. I then painted in several shades (starting with knarloc green, and using camo green IIRC maybe others too) of green, and brown (brighter than the end colour). I threw on a devlun mud wash with varying amounts. I let that dry. I then threw one a couple coats of 'ard coat to make it look all slimey and moldy. I also used mixes of green and brown in patches before the washes/'ard coat. Sometimes, while the green was still wet, I took the brown dipped it quickly in my water jar, and dabbed quickly in spots to make a nice blotch look.
For the plaguebearers itself I painted the flesh with elf flesh. I then either layered washes on there with mud, purple, black. Mud, purple, flesh… or mud, purple, mud. Yes, different plaguebearers got different combos. The purple is VERY important, as it gives a bruised look. Sometimes I only applied the purple in patches, others to the majority. The purple was also works very well on anything red.
Swords involved several shades of green, some highlight work (and I may add another step in highlighting).