Two rungs of white and techeiles

בענין לבן ותכלת הוא בחי' טהרה וקדושה כי התכלת בחי' קדושה והוא מעין הציץ של כ"ג דכתיב עליו קודש לה' והוא ג"כ על פתיל תכלת.

Regarding white and techeiles (the blue thread): this is the aspect of taharah (purity) and kedushah (holiness), for the techeiles is the aspect of kedushah, resembling the tzitz of the Kohen Gadol, upon which is written "Kodesh la-Hashem (Holy to Hashem)," and which is likewise set upon a pesil techeiles (a thread of blue).

The two colors of tzitzis correspond to two levels: the techeiles, the deep blue, represents kedushah, paralleling the High Priest's headplate that bore the words "Holy to Hashem" and was bound with a blue thread.

והלבן דרגא שלמטה בחי' טהור.

And the white is a lower level, the aspect of taharah (purity).

The white threads represent the more accessible, lower rung of purity, beneath the loftier sanctity of the techeiles.

וקרח שאמר כולם קדושים נטל טלית שכולו תכלת:

And Korach, who said "they are all holy," took a tallis that was entirely techeiles.

Korach's error was to claim everyone already stands wholly at the level of kedushah — a garment "all techeiles" — skipping the lower rung of taharah and the ordered ascent it requires.

Summary: The white and blue of tzitzis map two rungs — taharah (the white, the lower level) and kedushah (the techeiles, like the Kohen Gadol's "Holy to Hashem" tzitz); Korach's claim that "all are holy," symbolized by a tallis entirely of techeiles, was the mistake of grasping at total kedushah while bypassing the foundational level of purity.