Change the LEDs in a USB light to a custom colour.

Most USB lights come with cold-white LEDs in them, but sometimes it's nicer to have another colour like warm-white for general use, blue for studio use, red for night use or even UV for special effects. This is a video showing the swapping of LEDs in a common cheap dollar-store type of USB light.
Most of these lights use the little straw-hat type of LEDs which are widely available on ebay in a huge range of colours including red, orange, yellow, green, blue, pink, UV, cold-white and warm-white.
It's an easy hack/mod so you could even use a few with a cheap USB power supply and hub to make a decorative night light.