Devo ter aqui alguma coisa mal…
Já corrigi para:

E ele não me muda nada…
Tenho a config assim:
hass_theme:
name: Temas
options:
- Dark
- Lightblue
- Frontend
- Solarized
initial: Lightblue
icon: mdi:theme-light-dark
Dark:
primary-color: "#424242" # Primary (most of the UI)
primary-background-color: "#303030" # Primary background colour (dialogs, e.t.c)
secondary-background-color: "#303030" # Secondary background colour (main UI background)
paper-card-background-color: "#424242" # Card background colour
paper-item-icon-color: "#949494" # Icon colour
primary-text-color: "#FFFFFF" # Primary text colour
secondary-text-color: "rgba(255, 255, 255, 0.7)" # Secondary text colour
disabled-text-color: "rgba(255, 255, 255, 0.5)" # Disabled text colour
divider-color: "rgba(255, 255, 255, 0.12)" # Divider colour
paper-card-header-color: "#FFFFFF" # Card header text colour
paper-listbox-background-color: "#424242" # Listbox background colour
paper-listbox-color: "#FFFFFF" # Listbox text colour
paper-grey-200: "#616161" # Listbox selected item background colour
paper-toggle-button-checked-ink-color: "#1DE9B6"
paper-toggle-button-checked-button-color: "#949494"
paper-toggle-button-checked-bar-color: "#949494"
paper-slider-knob-color: "#949494"
paper-slider-knob-start-color: "#949494"
paper-slider-pin-color: "#949494"
paper-slider-active-color: "#949494"
paper-slider-secondary-color: "#949494"
O que estarei a fazer de errado?
Obrigado @souzaathales