how to modify this thing style

[WingDust]

[d13]

Those come from VS Code, not GitLens.

I believe those are the editorGutter colors, which you can find listed here: https://code.visualstudio.com/api/references/theme-color#editor-colors

Customizing theme colors guide: https://code.visualstudio.com/docs/getstarted/themes#_customizing-a-color-theme

Rough example:

{
  "workbench.colorCustomizations": {
    "editorGutter.modifiedBackground": "#ffffff"
  }
}