Some social button variations use outdated or wrong color codes, e.g.

• Twitter:
  • Official: #55acee (https://about.twitter.com/company/brand-assets)
  • Semantic-UI: #0084b4
• Pinterest:
  • Official: #bd081c (https://business.pinterest.com/en/brand-guidelines)
  • Semantic-UI: #00aced (light blue instead of red?)
• Google+:
  • Official: #dd4b39 (https://developers.google.com/+/branding-guidelines#googleplus-icon)
  • Semantic-UI: #dc4a38 (almost)
• Instagram:
  • Official: no single color (http://brandcolors.net, https://www.instagram-brand.com)
  • Semantic-UI: #49769c

I didn't check all social buttons, just the ones I needed. And it seems as if there are more social button variants defined than visible on the docs page http://semantic-ui.com/elements/button.html#social