Importing obj, some part of the model lost colors

I’m new to nomad (about 2-3 weeks) so sorry if this problem is known or already answered.
I made a model In nomad, I merged it into One object, without layers, etc. then I exported it as obj file, then opened it to see how it looks like if I send it to someone.
I noticed that horns have lost their color. I thought if I make models without layers, the colors remain but it only worked for some parts of my model. so i wanna know what’s wrong.
I’m not really familiar with texture concept, I didn’t use any. I just made a model and painted.

There is no texturing in Nomad, it’s only vertex painting.

Obj doesn’t support roughness/metalness vertex painting so you’ll lose this information.

It’s best to use glTF to transfer model in Nomad, it retains every information. (Some stuffs won’t be supported on other software, but it should always work fine in Nomad)