I believe this might help:
Set a variable to a string with the color name - this can be changed at any time so you can update colors whenever you need to. Simply add a [color=variable] .. text..[\color]
This video will go into some detail for you
https://youtu.be/wda5h_QcX5U
so I tried this solution but it seems that textareas don't support bbcode, but textinputs do like shown in your video. I would need to use a textarea for the automatic scrolling behaviour which is missing with textinputs.