This will 1) disable the search and 2) show all datetimes.
With regards to the calendar category colors, the calendar has a limit of 1 category per event in order to accurately set a category color for each event. When you assign multiple categories to an event the calendar scripts can’t discern which category to use (there’s no UI for this).
The category colors can be overridden with custom CSS. So if you can mention exactly which event you want to be a specific color, I can share an example of how to do that with CSS.