You can still export color-only materials using the new tool. To do so, you must chose your material mode to initialize the node tree. Once that's done, you can change the input of "base color" and "specular" to "RGB" and set the color. The specular highlights are a bit more tricky. With Blender 2.8 came a lot of changes to the material nodes, one of them was that they changed some parameters for specular materials. I remember that I had to remove some of the links between the fs material settings and the blender material to make it work, but that's quite a while ago and I can't remember the details. That being said, if you have an idea how we could link the fs settings to an appropriate Blender parameter, I'm happy to implement it in a future version.