After killing an infected bloodbug, which uses some sort of green textured shader, the shader effect appeared to be transferred to the player character's head.

Sample: my smooth-talkin', sharp-dressin' lady's man was transformed into this: http://www.designamatic.com/GraphicsFO4/FO4-WandererThreeWithGreenSkin01-Medium.jpg

Yikes! Fortunately a save and reload got rid of the extra shader effect.