Usually is used for links, main button, image overlay…
Usually is used for links mouse over state, secondary button.
Usually is used for heading (h1 – h6) color.
Usually is used for grey button, post quote format background, post link format background, page navigation, page break, pre…
Usually is used for top bar, header menu, posts loop, widgets, separated dividers in the single post, elements like (input, selectbox)…