Many harmful flying insects – whiteflies, fungus gnats, fruit flies, flea beetles, and aphids in the winged stage – are attracted to the color yellow. To take advantage of this, you can buy and place throughout your garden or greenhouse yellow sticky traps – small yellow squares coated with a nontoxic gooey material. But you can also make your own. Paint an old piece of glass or Masonite bright yellow and coat it with Tanglefoot. If thrips are a problem, use light blue paint.