This issue is a result of a short discussion with @punker76. We are using the ModernUI package in a couple of our WPF projects, because of the elegant look of (some) input controls and (TBH) I prefer some of the styling over the current MahApps styled controls.
Jan told me to list the controls I like from ModernUI and maybe he could do something in the future. The controls are in general pretty minimalistic, but it looks pretty clean and if you focus the control the highlighting is in the current accent color - pretty, right?
I really like the following controls:
Short demo:

TextBox and ComboBox are easily adjustable with this code:
<SolidColorBrush x:Key="TextBoxMouseOverInnerBorderBrush"
options:Freeze="true"
Color="{StaticResource AccentColor}" />
<SolidColorBrush x:Key="TextBoxFocusBorderBrush"
options:Freeze="true"
Color="{StaticResource AccentColor}" />
<SolidColorBrush x:Key="ControlFocusBorderBrush"
options:Freeze="true"
Color="{StaticResource AccentColor}" />
<SolidColorBrush x:Key="ComboBoxMouseOverInnerBorderBrush"
options:Freeze="true"
Color="{StaticResource AccentColor}" />
<SolidColorBrush x:Key="ButtonMouseOverInnerBorderBrush"
options:Freeze="true"
Color="{StaticResource AccentColor}" />
TextBox:

ComboBox:

That also looks a lot better in the dark theme, IMO the dark theme needs a rewrite anyways because some colors are just too bright.
@Alkalinee It's not only to change color, there are also some style changes... all in progress :-D and coming soon
@robertmuehsig Oh man, sorry, one year is long ( 馃様 ) ...
So here are my baby steps for this
Most helpful comment
@Alkalinee It's not only to change color, there are also some style changes... all in progress :-D and coming soon