John Shade: "A dark Vanessa with a crimson band/ Wheels in the low sun, settles on the sand/ And shows ink-blue wingtips flecked with white..." (993-5)
Charles Kinbote: "One minute before his death, as we were crossing from his demesne to mine... a Red Admirable...came dizzily whirling around us like a colored flame. Once or twice we had already noticed the same individual, at that same time, on that same spot, where the low sun finding an aperture...splashed the brown sand with a last radiance... One's eyes could not follow the rapid butterfly as it flashed and vanished, and flashed again, with an almost frightening imitation of conscious play which now culminated in its settling upon my delighted friend's sleeve...Then the tide of the shade reached the laurels, and the magnificent, velvet-and-flame creature dissolved in it."
 
JM: The quotes from Pale Fire describe the apparition of a Red Admirable, close to the end of Shade's poem and of his life.
Shade could not have written about it and,only then, got up to walk along with Kinbote for a knackle of nuts and a glass of Tokay,when he came across this same butterfly.What strikes me most in Shade's lines is how he brings up minute details, which he couldn't have seen from a distance, exceept through the eyes of his memory (the ink-blue wingtips flecked with white). 
Besides, the specific butterfly, his "dark" Vanessa (why dark?), settles with its wings open like a night-moth (otherwise the wingtips, as described, wouldn't be discernible).
 
Kinbote spins a different story altogether. He explains the insertion of the butterfly in Shade's poem, and their subsequent stroll cum Red Admiral, by informing,quite casually, that it was "the same individual" which both had encountered before in curious situations. He adds a mysterious and magical mood into his report, an "almost frightening imitation of conscious play".  He also creates a "phaneros" ( Boyd's Orphic Phanes, or "a flame that appears and vanishes...). He also exalts its red color, unlike Shade. Kinbote's "ominous" Vanessa is, indeed, a Red admiral, "a colored flame" or a "velvet-and-flame" creature.  Although he mentions the sand, like Shade did in his verse, and an approaching "tide of the shade" that "dissolves it" Kinbote's (insistently) flaming insect settles on Shade's sleeve, not on the sand.*
 
 
 

The third line is misquoted.  It should be "And shows its ink-blue wingtips flecked with white."

Here is a photo of a Vanessa on the ground:

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