DesignColors constructor Null safety

1. fact_browser
2. constants
3. DesignColors
4. DesignColors constructor

DesignColors class

1. Constructors
2. DesignColors
3. Properties
4. hashCode
5. runtimeType
6. Methods
7. noSuchMethod
8. toString
9. Operators
10. operator ==
11. Constants
12. backgroundBlue
13. black
14. green
15. lightBlue
16. lightGrey
17. pink
18. red
19. yellow