How do you hide/disable the active tab’s border color? In the screenshot below, it is the red line at the top of the tab:
>Solution :
By default, there is no color option specified for that (are you sharing a settings.json file?)
To remove the color of the top border, look at your setting.json and find workbench.colorCustomizations and within it, find tab.activeBorderTop and delete it:
"workbench.colorCustomizations": {
"tab.activeBorderTop": "#ff0000" //delete this line
}