@jpaul
This is not a job for Gimp. It says on the website as you referenced in your first post.
Material of old painted boards. The color is green by default, it can be changed in Composite Layers using a mask (disabled by default and also not available in FBX).
Remember Gimp is 2D editing, if the image is a bitmap and on the long-shot you can open your file in Gimp, you can change the colour in several ways but probably no use to you.
Bottom line, can you open the file ?
This is not a job for Gimp. It says on the website as you referenced in your first post.
Material of old painted boards. The color is green by default, it can be changed in Composite Layers using a mask (disabled by default and also not available in FBX).
Remember Gimp is 2D editing, if the image is a bitmap and on the long-shot you can open your file in Gimp, you can change the colour in several ways but probably no use to you.
Bottom line, can you open the file ?