color: easy way to generate color models by vertex to enter Blender

I procedurally model 3D planets that I would like to import into Blender.

I use color by vertex representation in my shaders (in practice, I use the same color for all vertices of a face, but my vertex attributes include RGBA).

I like to generate wavefront .obj Files, because the syntax is very easy. But the wave front obj does not allow me to specify color by vertex or color by face. Instead, the entire object is colored with a material from the material library that accompanies the obj geometry file.

I have looked at collada .dae also, but frankly, it seems a very complex format, and it still seems to work with libraries of materials, as does the .obj format.

Is there an easy-to-generate 3D model format that allows me to specify a color per vert (or face) without material libraries, and can it be imported into Blender?