Gainsboro

By using light gray or Gainsboro we are using Edward Tufte's principle of "minimum effective difference" to put in ancillary information.

When the temperature reached to^([sic]) about 40 °C, the color of characters began to change, and it changed completely from black to gainsboro when the temperature rose to about 50 °C. As the[…]film cooled down to the room temperature, the color returned to black.