How scientists colorize photos of space ?

We see colors becasue cells in our eyes called cones interpret light reflecting off of objects. Light is  a radiaton which means it has different frequencies, most of which are invisible to human eye. What we can see is called a visible spectrum, it appears red at it lowest frequencies and violet at its highest. This spectrum can be divided into 3 different cones which rougly corresponds to red, green and blue meaning that they are the primary colors of light and every other color is a combination of these three.
Every Hubble's telescope photo that you see actually started as black-and-white image. That's because its main function is to measure brightness of objects in space. Adding color to photos is pretty easy nowadays. You have to make 3 copies of the photo then apply red, green and blue filters onto them and combine them together using a computer program like Photoshop.
Scientists also use colors to find and map out chemical elements in space. Hubble can record very narrow bands of light coming from individual elements, this is called narrowband filtering.
When we look at a photo of unvierse we can see some colorful gas clouds, stars or planets but scientists can use the same colors that we see to track chemical elements or even some astronomical events which is truly fascinating.

source:https://www.youtube.com/watch?v=WSG0MnmUsEY