Color Settings should use color utility classes instead of inline styles

**Is your feature request related to a problem? Please describe.**
We've added Color Settings panels to the core List and Quote blocks, which allow for coloring of those blocks. The current implementation simply adds an inline style with the color applied.

**Describe the solution you'd like**
We should figure out how we could employ color classes within the save functions of those blocks, so that the color utility classes defined by the theme can properly declare the colors.

**Describe alternatives you've considered**
Gutenberg core may eventually add coloring to other text-based blocks, though there's no real timeline/expectation there.

**Additional context**