You need to set a light source. That would make your model look even more realistic. I suggest to use a directional light and ambient light. The warning appears because the unlit shaders are set in case no light source exists.
Difficult to say since I don't have the original model. Do you get the same warning in the Wikitude3D Encoder? Have a look at the material of the original model of these objects. Especially on the specular value. Could you provide the fbx/dae you used for encoding including the textures?
about 5 years ago
Some buildings are completely black.This message appears on Xcode console: bind -- Warning: Material parameter 'u_specularColor' not found in effect 'shaders/textured-unlit.vert;shaders/textured-unlit.frag;'