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Your date is different than you expected because of useUTC
API option which value is by default set to true. Because of that UTC time is used to calculate date based on provided timestamp. Setting that option to false should be what you are looking for.
API reference: https://api.highcharts.com/highcharts/time.useUTC
When it comes to that excessive spacing in exporting menu, to tell exactly what is the cause of that behaviour, I need you to provide me with working demo showing that issue. You can start here: https://jsfiddle.net/BlackLabel/6t0cvu5w/
If that spacing is somehow caused by Bootstrap, then I can't really help you with that, because the problem is not related to highcharts.
Regarding your question about inserting a color, I don't understand what exactly you want to achieve, some clarification would be greatly appreciated here. Chart colors can be changed via various available API options like backgroundColor or with CSS. You can also use one of few Highcharts color themes (this dark one might interest you: https://www.highcharts.com/demo/dark-unica
), or create your own theme.
More about themes: https://www.highcharts.com/docs/chart-d ... yle/themes
https://www.highcharts.com/docs/chart-d ... tyled-mode