Fix 3 hex codes shown on Colors page to match those in the css

[jstrothman]

On the Open Forest design system colors page the hex codes displayed on screen for the three $color-primary-alt greens are incorrect, i.e. they are shades of blue and don't match the hex codes in the css.

• $color-primary-alt should be #076727
• $color-primary-alt-darkest should be #073d11
• $color-primary-alt-dark should be #0a531b