"Well, when clothing is washed, the lint is lifted from the edges of the clothing, however, the water prevents it from being completely removed from the surface of the clothing. When the clothing is transferred to the dryer, this is where the magic happens. The heat from the dryer, along with the tumbling process, exacts these bits of fibers from the surface of clothing. These particles are then collected into the screen of the lint trap."
Why is it a muddy, dirty gray?
"The reason for the uniformity of color is that when you mix colors at random you end up with a muddy, dark mess. Melt a box of crayons together and you’ll see this for yourself. But when you mix clothes that are mostly blues, grays and blacks — as is typical with most wardrobes — with a smattering of reds, browns and greens, the mess becomes bluish gray every time. Essentially, the contributions of your blue jeans and white athletic socks outweigh those of your favorite red t-shirt."
What hobbies can lint be used in?
"If you’re feeling really crafty, you can lift a bit from some old wool sweaters you no longer want to wear and make felt.Just soak the sweaters in some hot water, wring them out and place them in the dryer. Thoroughly clean the lint catcher before drying the sweaters and the wool lint you gather will be excellent raw material for homemade felt."
"To use lint as a pet bedding option, take it a step further than just putting it into their cages or laying it on the floor. Simple sewing techniques can be used to create pillows or small pet beds for guinea pigs, hamsters, small dogs or even cats! Use the lint as a stuffing for a fleece pillow. This will create an extra warm area for beloved pets!"
You can find many more uses and more curious questions HERE