Why my model look different

I proceed to chapter 6 Texture.
There is a little problem not very critical . I build a model in blender ,but when I import it into my project and check it by click it in the file navigator, it shows complete white . see below
image
but when I check the models that the book provided it looks like this
image
at least there is some color on it!
why?

Have you set the vertex colors in Blender?

Xcode is often touchy in what it shows. It’s marginally better in USD format.

I set the vertex color , but there is no vertex color export option when I export obj format in blender
I compare the .mtl file of both there are similar . so what is the reason
image
could you please tell the meaning of abbreviation
kd ->diffuse
ks ->specular
ka ->ambient
ke->?
Ni->?
Ns->?
d->?
maybe the reason is related to the value of them !

USD format display well, can it replace obj , it does not have a .mtl file attached

.usdz (a zipped up .usd) is the preferred format now. As it’s fairly new, not all 3d apps output to it, but Apple does have a conversion at AR Creation Tools - Augmented Reality - Apple Developer

Here is everything about the .mtl format: MTL OBJ materials file

I’ve compared the train and cottage1.obj from chapter 7 in the Xcode scene editor, and the cottage has emission as white. If you turn it to black, then the colors show. I have no idea how the scene editor is reading the emission color, as the obj format doesn’t support it.

by adjust the emission to 0 , my model now looks good , thank you ,
image
the .usdz format not used in the book . so I leave it back and I will research it when I use it

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The animation chapter uses the .usdz format. .obj files can’t hold animated data.