If you prefer darker colored charts, right-click into the Window, select Properties, then choose Dark Theme from the dropdown.
If you would like the grey borders of your Trade Ideas Windows to be darker or differently colored, you can adjust them in the Color settings of your Windows Operating System.
Right-click into your Desktop area and select Personalize.
Choose a color from the color palette or add a custom color, then check Title Bar and Window Borders.
You might need to Restart Trade Ideas after you have made changes to your Windows color settings.
Thereafter the borders of an active Trade Ideas window will appear in your desired color.