Hi, @marie999!
To change the header color, you should go to Customizer -> Header -> Change Header Color, as you can see here. To change the color of a button, you should go to Customizer -> Header, click on the button, go to the Style section, expand the Normal option and choose the color, as you can see here. If you expand the Hover option, you can choose the color that will appear when you hover over the button. To change the color of the text from the menu, you should go to Customizer -> Header -> Change Menu -> Style and choose the colors you want for the text, as you can see here. Similarly, to change the color of the footer, you should go to Customizer -> Footer -> Change Footer Color.
I hope this helps!
Have a nice day!