How to use procedural light cookies (Blender Internal) I am trying to implement some of the tips in this lookdev article, and the first thing I tried is "noising up" my spotlights with a cookie.

I have figured out that all you really have to do is add a texture to a light.  But what I don't understand is how to noise it up without altering the light color.  What is the normal setting for light cookies that add slight intensity variation to a light?  Am I supposed to just set the color to grey?  Or is color supposed to be off and RGB-to-intensity chosen?  That only seems to work with colored noise.  Lastly, I assume it is like Ambient Occlusion where you want to darken with the multiply mode but I can't find tutorials either way.  Any help is appreciated!
The easiest way would be to put a sub-divided mesh in front of your light, with a multi-slot material bank associated to that mesh. Then all you would have to do in each material slot is give each their own alpha value, then do a random face selection for each slot and assign it to the selection.

Just make sure that your material is equally RGB (R=G=B) for each slot, and you won't modify the color, only the tint/intensity.