Updated changes.md and contributors.md

Author: markchagers

CHANGES.md

@@ -1,5 +1,8 @@
 # Change Log
 
+##### Changes PR https://github.com/CesiumGS/cesium/pull/9673
+- Changes type annotations for several color properties from Property|undifined to Color|undefined
+
 ### 1.84 - 2021-08-02
 
 ##### Additions :tada:
@@ -10,6 +13,7 @@
 - Fixed the ability to set a material's image to `undefined` and `Material.DefaultImageId`. [#9644](https://github.com/CesiumGS/cesium/pull/9644)
 - Fixed render crash when creating a `polylineVolume` with very close points. [#9669](https://github.com/CesiumGS/cesium/pull/9669)
 
+=======
 ### 1.83 - 2021-07-01
 
 ##### Breaking Changes :mega:

CONTRIBUTORS.md

@@ -294,3 +294,4 @@ See [CONTRIBUTING.md](CONTRIBUTING.md) for details on how to contribute to Cesiu
 - [Ethan Wong](https://github.com/GetToSet)
 - [Calogero Mauceri](https://github.com/kalosma)
 - [Ren Jianqiang](https://github.com/renjianqiang)
+- [Mark Hagers](https://github.com/markchagers)