In vanilla minecraft bed's no longer support railings by the leggings like you use to do in: previous the color update via the block. Even Windows 10 edition supports it. I tested it with solid black color on every single space besides default and compared it to windows 10 edition the result is that vanilla bed model cannot have the railings by default.

Windows 10 edition to the right showing railings
Previous 1.10.2 you could simply color per block 16x16 where you wanted what pixel not the case here and which you use to be able to get railings
Left shows a black bed all except for default and has no black railings regardless of windows 10 supporting it

I do not see the way to make the model this way or even how to change the vanilla bed model since they don't exist anymore.