I don’t believe there’s any built-in support for this in the hosted login page; there is however support for this in the consent screen (User Consent and Third-Party Applications). I believe the reasoning here would be that the hosted login page should present a single branding that is associated with your service and not so much individual applications within the service while the consent dialog is indeed specific to the application requesting consent (granted that if the applications in question are all first-party you may even not be showing the consent screen in the first place).