From WiKirby, your independent source of Kirby knowledge.
||On some stages you will find grayed-out areas where colors don't exist and rainbow ropes can't be drawn.
— Kirby and the Rainbow Curse electronic manual, page 13
A Gray Zone is an area of total color desaturation that can be found at various points in stages in Kirby and the Rainbow Curse, comparable to no-draw zones in Kirby: Canvas Curse. Within its area of influence, Rainbow Ropes cannot be drawn, meaning that Kirby will need to find another way to move forward through or avoid this area if possible. Gray Zones are often placed in areas that force Kirby to make use of his other talents, or may force him to approach the area from the outside in a more creative manner in order to get through it without issue. Usually, valuable items can be found in or past these zones, making them more challenging to obtain in most cases. Naturally, though Rainbow Ropes cannot be utilized within them, Kirby still has access to his other abilities within the Gray Zone, including Touch Dashes and Star Dashes.