Thank you Stefan Blom. From the preview they give in Edit Theme Colors, it is just not clear what color applies to what. The first two text colors work as suggested on the image I posted, but the second two text color options do not work in any theme or combination of text and background. The use of Accent colors is not clear to me either. Except for pie charts I haven't seen what's the use of Accent colors 2-6 with shapes, tables, borders or similar. In fact, when I use certain shape for example, and if I use a specific theme, to paint it in specific color, it is going to be painted in Accent 1 color of that theme, and the border will be a lighter shade of that same color, decided arbitrarily by Word, not according to any settings of Accent colors I have chosen. When I manually change Shape fill color, for example, in Drawing tools --> Format, that color will change when I change themes, but not the Shape outline color, if I manually selected the specific border color.
All in all, I'm confused about the use of colors for anything in Word, and when I try to customize themes, I'm never sure what will I get in the end, which is frustrating. I wish I could use the color theming in Word more effectively.