Excess elements in struct initializer when nested std::array

I'm getting Excess elements in struct initializer on the return line of the following:

using triangleColor = std::array<std::array<float, 4>, 3>;

triangleColor colorBlend(TriangleColorBlend c){
    switch (c) {
        case TriangleColorBlend::white:
            return {{1.0,1.0,1.0,1.0},{0.7,0.7,0.7,1.0},{0.5,0.5,0.5,1.0}};
            break;

        default:
            break;
    }
}

I was hoping the curly-brace literal would work in the nested fashion, as it works fine if I do this with just a single std::array, not nested.

Is the above simply not possible, and why not?