How to change vuetify widget params in Trame Python

I'm truing to make a simple GUI with Trame. And finally managed to make 'File' menu items.

from trame.app import get_server
from trame.ui.vuetify import SinglePageLayout
from trame.widgets import vuetify
import asyncio

server = get_server(client_type="vue2")
state, ctrl = server.state, server.controller

state.file_menu_items = [
    {'type': 'header', 'title': 'Light Guide',},
    {'type': 'item', 'title': 'Load', 'value': 'lg_load',},
    {'type': 'divider'},
    {'type': 'header', 'title': 'Project'},
    {'type': 'item', 'title': 'Load', 'value': 'pj_load',},
    {'type': 'item', 'title': 'Save', 'value': 'pj_save',},
    {'type': 'divider'},
    {'type': 'item', 'title': 'Exit', 'value': 'exit',},
    ]
def file_menu_item_click(value):
    if value == 'lg_load':
        print("Light Guide Load")
    elif value == 'pj_load':
        print("Project Load")
    elif value == 'pj_save':
        print("Project Save")
    elif value == 'exit':
        print("Exit")
        asyncio.create_task(server.stop())
ctrl.file_menu_item_click = file_menu_item_click


with SinglePageLayout(server) as layout:
    layout.title.set_text("Ray Tracer GUI")
    with layout.toolbar:
        vuetify.VSpacer()
        with vuetify.VMenu():
            with vuetify.Template(v_slot_activator="{ on, attrs }"):
                with vuetify.VBtn("File", dark=True, color="primary", v_bind="attrs", v_on="on"):
                    vuetify.VIcon("mdi-menu-down")
            with vuetify.VList():
                for item in state.file_menu_items:
                    item_type = item.get('type')
                    if item_type == 'header':
                        vuetify.VSubheader(item['title'])
                    elif item_type == 'divider':
                        vuetify.VDivider()
                    elif item_type == 'item':
                        vuetify.VListItem(
                            item['title'], 
                            click=(file_menu_item_click, f"[\'{item['value']}\',]",),
                        )


if __name__ == "__main__":
    server.start()

But I want the active element to be not grey as it is but for instance blue. How can I do it? color property doesn't change anything. Also may be somebody can explain me what does

vuetify.Template(v_slot_activator="{ on, attrs }")

mean?

And finally may be you can recommend some text except docs where the logic of Trame and its interaction with Vuetify would be expained?