Blender mesh when exported into roblox, come out as gray

I exported the mesh as an obj file and imported it into roblox. I used vertex paint to color it, yet for some reason, when I imported it into roblox, it just came out gray. Please help! (im using newest version)

use .fbx instead .obj for vertex, i dont really know if .obj suports vertex paint.

all the times i used vertex paint and imported to roblox i used .fbx files

I used fbx, didnt work.