And I'll reiterate that unless I'm missing something, it'd be simple enough to achieve an identical visual look already. Create your skybox model, UV it by relaxing everything so all vertices are as spaced apart as possible, then bake your vertex colors into a texture, which can be pretty small. After that, all you need is to 1) modify the vertex shader so that for all skybox models, the shader samples the texture at the vertex position and sets a varying, and 2) modify the fragment shader so that for all skybox models, it uses the aforementioned varying to color the pixel with.