Assignment of textures to Material via code does not update the Material.

Symptoms

• Assignment of textures to Material via code does not update the material. It is necessary to open the Material in the Inspector tab.

Cause
If you use scripting to change a Material that would cause it to use a different variant of the Standard Shader.

For example assigning a Normal Map to a Material that did not have one, or setting the Emissive level to a value greater than zero, when it was previously zero.

Resolution
You must enable the Standard Shader variant by using the EnableKeyword function. A different variant would be required if you start using a shader feature that was not initially in use by the material. 

The specific Keywords required to enable the Standard Shader features are as follows:
_NORMALMAP (Normal Mapping)
_ALPHATEST_ON (“Cut out” Transparency Rendering Mode)
_ALPHABLEND_ON (“Fade” Transparency Rendering Mode)
_ALPHAPREMULTIPLY_ON (“Transparent” Transparency Rendering Mode)
_EMISSION (Emission Colour or Emission Mapping)
_PARALLAXMAP (Height Mapping)
_DETAIL_MULX2 (Secondary “Detail” Maps (Albedo & Normal Map)
_METALLICGLOSSMAP (Metallic/Smoothness Mapping in Metallic Workflow)
_SPECCGLOSSMAP (Specular/Smoothness Mapping in Specular Workflow)

More Information

Please see our Manual for more information.

This articles applies to Unity versions 5.0+