Create a new `Color` method in the `Temperature` class in `SimpleWeatherService` for easier reusability.

[JustScott]

It was brought up in #2204 to move the TemperatureColor function to the Temperature class in SimpleWeatherService as an easy to reuse method, however since then it has been decided to use a static temperature color in the terminal watch face instead which means the TemperatureColor function is only used in one file (weather.cpp) making it currently "pointless" to move this function. However, I'm still creating this PR in case others think we should still move this function to the Color method for easy reuse in the future.

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