Cause found: ipf_chest215.plt uses the wrong background luminance.
Expected transparent background pixel: FF 00
luminance 255, Skin layer
Actual background pixel: FE 00
luminance 254, Skin layer
All background pixels use FE 00 and form one border-connected region. In pal_skin01.tga, luminance 254 is opaque, while luminance 255 is the transparent endpoint. This makes the background render nearly white instead of transparent.
The PLT header and dimensions are valid (PLT V1, 64×128). The safe correction is to change those border-connected FE 00 pixels to FF 00.
Also, ipf_chest212, 213, 215, 216, and 217 are byte-identical, so they likely share the same background bug.
