Texture coordinate sampling in cg surface shader

Hi, I'm trying to sample the color from a procedurally generated texture in a surface shader. This is a self-contained, simplified version that demonstrates the issue.

Brief: I have a texture that looks like this.

I'd like the texture to be 2x2 pixels, but I have tried various sizes to make sure it wasn't a size issue.

What I want to do: I'm trying to sample each pixel and get the exact rgba value in order to do some fancy stuff in the shader with.

Problem: If I turn OFF both the FilterMode.Point and the TextureWrapMode.Clamp, every texture coordinate retrieves a blend of all of the colors, but as long as either or both are ON, it only retrieves GREEN or WHITE.

How I'm doing it:

I create the texture in code like so.

 opsTex = new Texture2D(size, size, TextureFormat.RGBA32, false, false);
 opsTex.filterMode = FilterMode.Point;
 opsTex.wrapMode = TextureWrapMode.Clamp;

I apply the texture using SetPixels and Apply on the texture itself, then assign the texture to the material.

 opsTex.SetPixels(opsTexColors);
 opsTex.Apply(false);
 renderer.material.SetTexture("_CoolTex", opsTex);

Inside the shader I retrieve the value via a simple tex2D lookup. Here it's being applied to the Emission just so it's easily visible as to what color value it's retrieving.

 float2 coord = (0,0);
 o.Emission = tex2D(_ProceduralTex, coord).rgb;

I change the value of coord around to get the color I want.

These are the values I SHOULD get:

 coord = (0.25,0.25) :: GREEN
 coord = (0.25,0.75) :: BLUE
 coord = (0.75,0.25) :: RED
 coord = (0.75,0.75) :: WHITE

These are the values I ACTUALLY get:

 coord = (0.25,0.25) :: GREEN
 coord = (0.25,0.75) :: GREEN
 coord = (0.75,0.25) :: WHITE
 coord = (0.75,0.75) :: WHITE

Conclusion: What am I missing? My mind is sufficiently boggled. Seems to me like the texture coordinate should give me exactly what it is displaying at that point, but it's not.

Thanks for any help.