Problem is that not all root variables are handled to have colors to stand out. I'd call it a bug. But it's kind of Royal size.
See that v-toolbar uses --v-theme-on-surface-variant: 238,238,238; for background.
If you change dashboard group background colors this is not changed. Thus it can't be visible in every condition.
Such things will happen if root variables not adjusted as theme but one by one. That bug should be reported but as dashboard doesn't provide all possible vuetify elements - who knows what to test against what kind of widget --- well, currently it's a mess.
61 colors to manage ...
Of course you can override those for now.
.v-toolbar{
background: ...
color: ...
}
