IPA: /ʌnˈdaɪd/
KK: /ʌnˈdaɪd/
Not colored; having the original color without any dye added.
The fabric was left undyed to showcase its natural beauty.
Undyed is formed from "un-" (meaning not) and "dyed" (from Old English "dīgan", meaning to color or stain). The word "undyed" means not colored or stained.
Think of 'not' ('un-') coloring something — that's why undyed means it hasn't been colored.