How Can I Use Javascript to Fill Shape Background Color with Hex Code?

On my PDF I have one form field where someone can input a hex code and to the right of that I have another box.

If possible, I would love to use Javascript to make it so when someone inputs a hex code it changes the fill color of the box to the right with that color.

Here is a screenshot of my PDF:

I'm not sure if this is possible, but fingers crossed it is

Important to note I have a very basic understanding of Javascript.

Thank you for your help,

Eric