You need to UV map your objects. Without UV mapping, the hardware has no way of knowing how to apply the texture, so you just get a solid color. The built-in cube is UV mapped.

Hi Jaimse,

I don't use .obj much, but I threw one I had lying around into Unity and applied a texture no problem. The normal workflow is to create a material first, unless you already have one from your 3d app, then set its texture and apply the material to the mesh. Don't confuse materials and textures. Materials define how your object looks through properties such as color, texture and which shader you're using. However, Unity usually creates a material for you if you don't have one when you apply a texture straight to an object, so I don't see how you would have problems. Do you see a material in the Project View?

As for changing textures at runtime, look up renderer.material.mainTexture. The following assigns a texture to the object this script is attached to when it is initialised (myTexture being the texture you've chosen in the Editor):

var myTexture: Texture2D; 

function Start(){ 

    renderer.material.mainTexture = myTexture;
}

See the Docs: http://unity3d.com/support/documentation/ScriptReference/Material-mainTexture.html

While the following assigns a texture through code that is stored in the resources folder (example from the Docs):

// Assigns a texture named "Assets/Resources/glass" to a Plane.
function Start () {
    var go = new GameObject.CreatePrimitive(PrimitiveType.Plane);
    go.renderer.material.mainTexture = Resources.Load("glass");
}

http://unity3d.com/support/documentation/ScriptReference/Resources.Load.html

Hope that helps, sorry I don't have an answer for why your texture isn't showing up.