To customize your theme, you can create a new theme that inherits from "theme-triton" and define your own SCSS file with custom colors. For example, you can set
$form-field-focus-border-color: #ff1744
to change the border color of focused items in a form.
For detailed instructions on creating a custom theme, check out this resource.
If creating a custom theme is not desired, you can directly modify the CSS classes applied to the specific element you wish to change:
.x-form-trigger-wrap-focus{
border-color:#ff1744 !important;
}