Update colors in docs.json

[ethanpalm]

Documentation changes

This PR adjusts the colors prop in our docs.json to use greens from our design system that have better contrast. This meets WCAG AA for colors.primary and colors.dark on light background, and WCAG AAA for colors.light on dark background, colors.dark. This fails contrast requirements for colors.dark on a dark background, but there is currently no way to achieve WCAG AA for colors.dark on light and dark backgrounds.

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