Thanks Charles, it wasn't until now that I finally understood what you meant, although it was after some trial and error.
The colour palette that appears when you try to change text colour is the same than what you see when trying to change theme colours:
Theme colours Dark and Light 1 to 2 are marked as D/L 1-2; Accents 1-6 are A1-A6 on the right picture.
Changing, say, Accent 1 to cyan means that the first square from A1 will be your selected colour, and the row below will be comprised of different shades of cyan.
If your Title was Orange from the 3rd square in A2, and you change Accent 2 theme colour to purple, your Title colour will change to the 3rd shade of purple.
I hope I could make this understandable to anyone with the same inquiry.
Thank you both!