Many shaders use more than one color. Use GetColor to get the propertyName color.
Common color names used by Unity's builtin shaders:
"_Color" is the main color of a material. This can also be accessed via color property.
"_SpecColor" is the specular color of a material (used in specular/glossy/vertexlit shaders).
"_EmissionColor" is the emissive color of a material (used in vertexlit shaders).
"_ReflectColor" is the reflection color of the material (used in reflective shaders).
Additional resources: color property, SetColor, Shader.PropertyToID.