Thirteen fabrics are each dyed with either indigo, or 6-bromoindigo, or 6,60-dibromoindigo. When the
dyed fabrics, which had not undergone any finishing procedures, are boiled in water for 10 min, color
changes are observed: many indigo- and 6-bromoindigo-dyed fabrics turn more blue, while many 6,60-
dibromoindigo-dyed fabrics turn more red. These color changes are characterized by reflectance spectra
and colorimetry data. Evidence is presented that the color changes are related to particle sizes of the
dyes: 6,60-dibromoindigo-dyed carbon nanotubes, used as a fabric surrogate, show an increase in dyeparticle
size upon heating, as judged by electron microscopy. Because we have shown previously that
6-bromoindigo-dyed carbon nanotubes give decreased dye-particle size when heated, we infer that, no
matter the indigoid or fabric, smaller particles tend to cause a bluer fabric shade, while larger particles
cause a redder shade