What? For the last 15 years, XC have operated fleets of Voyagers, Turbostars and HSTs all in the same livery with the same branding, how do you come to the conclusion that they've never liked having a consistent brand?
With respect everyone is entitled to their own opinion and no opinion is right or wrong within reason. Now going back to your question, the Voyager fleet has had Virgin XC interiors their entire working life, even when they received a minor interior refurbishment XC still kept Virgins interior colours on the seats and carpets. Bare in mind XC has held the franchise since 2007. Then we go to their advertisements and social media, often it's chaotic especially their social media a few years ago, they behave more like a budget airline than a major intercity rail corridor connecting the South of England with the North.
To bring everything back into the context of the thread, if you look at the renderings for the new Voyager interior, it's all black seats, cyan and pink grab poles. Compared to the Turbostars which have kept the red grab poles and a similar style moquette in standard. Take a look at operators such as Great Western Railway, nearly every train as the same interior/exterior has the same appearance, the branding is well presented and the advertisements have become a staple of the brand. I do hope when XC eventually joins GBR the the North-South corridor will be treated with a bit more importance than it has done under the last 20 years with Arriva.