Thank you.
I updated ColorWell to v7.1.4 and it works fine now.

ColorWell is seated in my menubar.
When I open ColorWell the first time, it's working fine.
When I type a hex code the color in the background is colored according to the hex code.
After I finished the colouring work I close ColorWell.
The next time I open ColorWell, I can type the hex code, but the background color no longer changes and also the rest (Color name, RGB, HSL, HSB, Lab and CMYK) aren't updated anymore.
In fact a change in any field no longer updates the rest of ColorWell.
I have to quit ColorWell and start the application to make it work again.
Unfortunately the process repeats itself (start reading from the beginning of the text).

Selecting a color by using the color picker does work, but I often work with hex codes and less with the color picker.

Mac mini (late 2012) 16GG memory
macOS 10.14.3 Mojave
ColorWell v7.1.3

I bought ColorWell recently and I like it very much and have it now constantly in my menubar.
There is 1 addition to ColorWell that would improve user experience more perfect to me.
The possibility to pick a color directly from the menubar without having to open ColorWell first.
Using a shortcut to activate the color picker would make it perfect for me.
(I refer to color picking like in apps as Sip or ColorSnapper)