Scene editor guide. Page 5

Lights - color

You can change here three sets of colors. You determine each color setting the quantity of Red, Green and Blue light that composes the light. This way actually you determine also the intensity of the light.

The ambient light is the one that is reflected by the object regardless of the light position. The quantity of reflected ambient light depends on the setting of the ambient material property of the objects.
The diffuse light is reflected based on the direction of the light relative to the object and the setting of the diffuse material property of the object. The specular light is reflected based on the direction of the light relative to the object, the setting of the specular material property and the value of the shininess of the object.

By default new objects has the specular material property set to (0,0,0) so you will see no effect changing the specular component of a light until you change the specular property of at least one object in the scene.