The phrase "blue light" refers to the light that is emitted by electronic devices such as smartphones, tablets, and computers. It is called "blue light" because it has a high concentration of blue wavelengths. Full definition
There's also a custom option where you can manually control the amount of blue light emitted from the screen, and set different colored backgrounds to your preference. (blog.the-ebook-reader.com)
This suggests we can help kids by using blue light filters and monitoring their access to technology. (parentingscience.com)
It makes the screen get warmer closer to your bed time in order to reduce the amount of blue light emitted from the screen. (pocket-lint.com)