Add value slider to your widget

The value slider is used to determine how bright/dark your final color is. A value of 0 is black while 1 is white. So for example if you pick a red color in your color wheel and choose with the slider a value of 0.2 it results in a dark red color.

To add the value slider to your widget just search for ‘slider color’ and add it to your widget:

Regarding the sizing you cannot make that much wrong compared to the color wheel.