A coloring blanket looks like a regular throw, except the design is printed as outlines that you color in yourself. Many come in a size of about 59 x 50 inches, with markers packed alongside.
You pick a section, color it, and come back to it another evening. Because the blanket is wide, two or three people can work on it at the same time.
Patterns range from flowers and fruit to cats, food or retro game themes. Choosing the design is half the fun, so it is worth looking at the whole pattern before picking.
The part people ask about most is washing. According to manufacturers, washable water-based ink comes out in a normal machine wash, leaving the printed outlines ready for a new round. Check the care label before the first wash.
Permanent fabric markers do the reverse: they are meant for a design you want to keep, and they do not wash out. It helps to decide before you start which parts should be permanent.
Two small tips before you start. Lay the blanket flat on a table rather than on your knees, and put the caps back on the markers between sessions. Start with lighter colors; darker ones are easier to add on top than to take away.
For adults, it is a calm evening activity away from screens, in the same spirit as coloring books. It is also a common gift idea for the holidays, since it is useful long after the coloring is done.