1:6
Some fabrics have a lot of excess dye which can cause discoloration
on other fabric but also on your sewing machine. This discoloring
may be very difficult or impossible to remove.
Fleece and denim fabric, especially red and blue, often contain a lot
of excess dye.
If you suspect that your fabric/ready-to-wear garment contains
a lot of excess dye, always pre-wash it before sewing to avoid the
discoloring.