ok, jig colour is the colour of the outer cloth and
the colour of the under tape is the the colour of the foil underneath the cloth.
if you look at your jig closely theres a second colour underneath the cloth, this is the reflective tape, this is what gets the squids attension first from a distance like the shiney sticker on a hard body lure.
anyway they make a guide for all the undertape/foil colours to maximise light/uv reflectiveness in all different conditions.
easiest way to remenber,
gold foil -morning & afternoon,
middle of day - rainbow,clear,silver foil,,
night time - red foil, glow
dirty water -white colour
but this is only a guide, you can still catch squid with red foil in middle of day, theres no right or wrong