Use <figurecaption> for <figure> captions (duh!)
Slightly darker text colour for better contrast

WCAG 2.0 recommentds 3:1 contrast
- http://www.w3.org/WAI/WCAG20/quickref/#qr-visual-audio-contrast-without-color
- http://www.w3.org/TR/2014/NOTE-WCAG20-TECHS-20140916/G183
- http://leaverou.github.io/contrast-ratio/#%23959595-on-white