Based on the below post and this apparent sense GBR is going to be a background thing for a while yet, here's an idea of what might happen....
There won't be a GBR livery until there are new train fleets being introduced. And it will only be applied to new trains until it's on half the fleet, then the remaining legacy units will be rebranded.
Before then, you can expect maybe only one off liveries to promote new fares and other major changes specifically announced and delivered by this Labour Administration in pursuit of its rail policy.
However, certain toxic brands might also get phased out, to be replaced by a very minimalist scheme. Maybe white with just a thin relief line and a small double arrow logo. Nothing brash, just subtle. Maybe in regional colours. Green for southern etc.
This will solidify on the minds of the public the connection of the GBR brand/s with the turning of the page, Starmer's promise. And for those paying attention, the benefits of a publicly owned railway being able to offer the private railway industry a planned and thus smoothed demand for new trains, to be rolled out with other Route level upgrades.
Looking at this from a political point of view; renationalisation is popular with the electorate, it was in the Labour manifesto.
The PM will want to show everyone he's delivering on his promise. Therefore I think a few units will get the new livery on day 1. It's a political tap-in, to use a football phrase.
I think you might be misremembering.
Here's the political dimension of railway renationalisation as I see it....
It was Jeremy's idea, a way to differentiate his new vibrant back to the grassroots Labour from the tired old spin machine and a man who couldn't eat a bacon sandwich (and I bet most people still dont realise he is now actually Energy Minister!). It was wildly popular, but evidently not so popular people were willing to overlook his alleged support for Hamas and all round revolutionary vibes.
It also wasn't exactly a smooth ride for Jeremy. He got caught allegedly spreading disinformation about one of our nation's most successful business leaders. So people got a massive reminder that this fantastic policy might not be grounded in reality at all. It might be just Jeremy playing on the naivety of people too young and stupid to have never even researched just how bad things were under British Rail. Something inextricably tied up with how bad things were under 70s Labour. Jeremy's brand. His general aim being to bring the band back together.
Last but not least, it was under Jeremy that it was first decided that for all the hopplah and razzmatazz of "Bring Back British Rail", they were only going to take back TOCs, and only as they expired. The kids didn't care because they didn't really even know any of that meant. But for wise and wizzened voters, it must have been very underwhelming. Adding to Jeremy's poor performance when it mattered.
So unless he's very careful, if he tries to wrap himself up in some brand relaunch, Starmer could end up needlessly reminding people about lots of bad things about various iterations of Labour. Reminding people it's not a very transformative policy, and it wasn't even his policy. Reminding people he purged Labour of the man who came up with it, and everyone for whom it was priority number 1. Absolutely symbolic of the revolution.
Reminding people that there's no way Jeremy would have been this slow to get things moving on GBR. Reminding people Starmer, like Jeremy, has already put out out several spin heavy statements regarding this policy. Announcing the Hitachi order for an open access operator, for example. I'm pretty sure they're not going to be in GBR livery eh?
Reminding people that Starmer's Labour is a lot more bacon eater and call me Tony that is or ever will be a real movement for real change. It is what it appears to be. Slow and steady. Not exactly in a rush on railways in particular. Last but not least, people know exactly what Starmer is trying to do when he stands behind Union Flags for the cameras, so it really won't wash if he stands behind a Union Flag adorned train.
He might not dare risk even doing it until he is absolutely certain that train won't be cancelled due to a driver shortage, points failure or strikes in its first month of service.