Color documentation review and update

[foxintherain]

What

Content review and improvements of color styleguide documentation for all brands to identify and improvements needed or gaps.

Why

Color documentation was created a while ago and needs a review.

Done when

• [x] Content has been reviewed
• [x] Improvements have been made
• [x] Updates have been reviewed by UI design team
• [x] Updates have been reviewed by Elements team
• [x] Updates published

Anything else

https://elements.springernature.com/springernature/styleguide/color

[foxintherain]

Starting with Color to consolidate with the a11y guide:

Color https://docs.google.com/document/d/1oBV4LOYTaYJIvz22jw9gVRzrEX_aMLvpEwdkqBQtkFc/edit#

A11y guide for Springer Nature colors https://docs.google.com/document/d/10XVU0kioJB1b3l2OkKXDF7AX2DqCzbq1tMNdN2RLyco/edit#heading=h.hm5cyteizv7c