Here’s a quote from my book Twin Peaks: Unwrapping the Plastic, which was published at the end of 2016, before the third season aired, and in which I discuss the opening credits of the original series: “The overall impression conveyed by the colours used in the opening credits is rather like a photo faded over time with several warm moments associated with the bird and the mill (reds and yellows). In contrast, the written text is a somewhat jarring neon green. This colour code can be linked to ideas found in Charles Webster Leadbeater and Annie Besant’s Thought-Forms (1901). Leadbeater and Besant were leading theosophists who endeavoured to give meaning to emotional dispositions based upon the colours present in a person’s aura, claimed to be seen by clairvoyants as an energetic field of light surrounding living things. The result of Leadbeater and Besant’s work was an ‘iconography of psychic conditions’ as described by Moffitt, who argues that perhaps Marcel Duchamp was influenced by this code in the creation of some of his paintings, as fellow artists Wassily Kandinsky and František Kupka certainly were” (p.44).
As we now know, the Thought-Forms in question have played a major role in The Return in the form of Tulpas.
Based on the concept that “thoughts are things”, the Though-Forms book presents a table of colours linked to certain feelings and emotions. Understanding these colours is necessary to properly read peoples’ auras. The book is replete with notions of vibrations, auras and radiations which, of course, make perfect sense in relationship to Twin Peaks.
Here’s the table of coulours included at the beginning of the book:
I believe this table becomes interesting in relationship to the colour of the nails of the main Tulpa of The Return, Diane. The importance of her nail polish is further underscored by the way she decorates her cell phone and also by Gordon Cole’s little game with Tamara’s nails in the plane. Is it possible the choice of “the” Nine Inch Nails” in episode 8 was not totally was not entirely coincidental either?
Deciphering the meaning of Diane’s nails in relationship to this colour table is not a simple task, but the overall feel is nevertheless a negative one. The colours she wears don’t exactly stand for positive thoughts or emotions.
Thumb = Depression
Index = Selfish Action
Middle Finger = Deceit
Ring Finger = Pure Affection
Little Finger = Malice
This analysis is of course far from definitive as it would require much better quality images of both Diane’s nails and of the table of colours from Thought-Forms. Nevertheless, I believe it already points towards certain elements of Diane’s personality that sound rather in tune with her character in The Return.
I will continue this research in the coming weeks, taking the time to read Leadbeater and Besant’s book more thoroughly, but this first approach enables one to get a first hint of what Lynch and Frost were trying to do with Diane. Reading her aura, i.e. her nails, might have been a very helpful tool in order to understand her true deceitful nature.
ADDENDUM: During a chat dedicated to Twin Peaks, Jean-Sébastien Chauvin, who works for the French film magazine Les Cahiers du Cinéma, told me that David Lynch went as far as to create a colour specifically designed for Diane. This information supports my argument, given that her nail colours were anything but random and represented a carefully planned colour palette.
TWIN PEAKS - Unwrapping the Plastic 
Just thought I’d add that Diane’s cell phone cover is an existing design, it’s Orla Kelly, relatively ubiquitous mid-range accessories designer. She tends to use these somewhat vintage, greyed-out multicolor palettes.
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Oh, also, I noticed in one scene that Diane has one single gem or perhaps a white or light blue paint dot in the middle of her right-hand thumb, over the dark-green base color.
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