Can I give one section's heading its own colour or a gradient?

Yes, per section.

1. Open the section and stay on the Content tab.
2. Click the small colour icon at the right of the Heading label.
3. In the Text Colour box, choose:

• Solid Colour: pick one colour.
• Multi Colour: a gradient across the heading.
• Image Fill: the letters are filled with a picture you choose.
• Default: go back to the theme colour.

1. Click Save.

The same icon appears beside Subheading and Description on many sections. Store-wide colours stay under Appearance → Color Settings and aren't affected.