I would like to implement a ColorPickerView Controller in my app like this in the picture.
But I don't know what this circle element is called and may I make that object bigger?

I have encountered a ColorPickerViewController that is presented modally as a complete another scene but at this moment, I would like to implement a color picker as a little window without opening a new window. Please, tell me how I can implement this.
I don't think it's possible to do that without opening it modally. That is the UIColorPickerViewController in UIKit, or ColorPicker in SwiftUI. It looks like this in iOS 14.
and in iPadOS 14 it would look like this
In SwiftUI it can be created like this:
}
and in UIKit it is like this
For more information you can take a look at these websites:
UIKit: https://www.swiftpal.io/articles/how-to-use-uicolorpickerviewcontroller-in-swift
Swift UI: https://www.hackingwithswift.com/quick-start/swiftui/how-to-let-users-select-a-color-with-colorpicker
Now Additionally, if you really want it to be in a little window, you can use a PopOver and create your own color picker, it is a bit of work but shouldn't be too hard.
Here are some resources that might help you: