add missing color yellow

[michaelknoch]

Type of change: feature

Motivation (current vs expected behavior)

https://developer.apple.com/documentation/uikit/uicolor/1621953-yellow

Please check if the PR fulfills these requirements

• [ ] Self-review: I am confident this is the simplest and clearest way to achieve the expected behaviour
• [ ] There are no dependencies on other PRs or I have linked dependencies through Zenhub
• [ ] The commit messages are clean and understandable
• [ ] Tests for the changes have been added (for bug fixes / features)