Hello @gozdehan,
In the shortcode you are referring to, the event color is not designed. To set your desired color for the whole MEC on your site, please head over to MEC Settings > Styling options and set your desired color: https://webnus.net/dox/modern-events-calendar/styling-option/. This is what gets changed: https://i.postimg.cc/fTr64ffw/image.png.
If you want to use the colorful calendar, you can use Novel skin: https://webnus.net/modern-events-calendar/monthly-view-novel-style/.
If you need a new shortcode, please submit your requests here: https://webnus.net/feature-request/, and if your request is already submitted, you can vote for it.
We would check them, and the one with votes would be selected to be included in the next updates.
Best Regards