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.
Designs vary a lot: dense floral patterns for long evenings, bigger shapes for kids or beginners. Large open areas go faster; small detailed zones take longer but look striking when finished.
The part people ask about most is washing. Washable markers use water-based ink that, per the manufacturer, washes out in the machine, so you can start over. The care label remains the reference for temperature and drying.
Permanent fabric markers do the reverse: they are meant for a design you want to keep, and they do not wash out. Just keep track of which areas were done with which ink.
Two small tips before you start. Color on a flat surface so the fabric does not stretch, and close the markers after each session so they do not dry out. A quick test on an edge shows how strong each color looks on the fabric.
For adults, it is a calm evening activity away from screens, in the same spirit as coloring books. As a gift, it works for people who like crafts but already have plenty of coloring books.