If you take a look to the provided screenshot you'll see what's wrong at first sight.
If you add a numeric input belong other kind of input.
You will see that the numeric input is the only one control to have a style which look like the control is being focused.
the NumericInput color is using the accent color for all states. We can't guess whether the control is focused or not.
the numeric input should have a default color and use the accent color only when focused. Use the default entry style for the entry of the numeric input.
you can also expose a numericButtonStyle property or some bindable property to allow us to set the color.
Right now, the control is unusable because of its look. Too bad, the implementation behind is nice.
It was better to create my own control which does the same. I use Telerik to avoid that.
Have a good day and thanks for your attention.