Radeon is a valuable, well known and established brand, there's no chance they'll not use it IMO.
I think it has as much baggage associated with it as good though. The brand loyalists will probably stick with AMD regardless of what they call their product, but I think there are a lot of people who still associate Radeon with bad drivers or who view it as the inferior product that you buy if you don't get a GeForce (NVidia) card. I question if that's worth keeping.
I'd argue that this works for some products, and not for others. Is there a market for GPUs where power efficiency is promoted as the chief quality? I wouldn't think so - power efficiency in the GPU space is a means to increase performance in a given power and thermal envelope. So the "green" label has no market value there.
Green would just be the low-power chips. There's already sort of a natural association with green and environmentally friendly. They need not even be the most efficient in reality, this is just a way of marketing cards to consumers. That marketing has pretty much already been done.
Then there's the competing "oh, this must be fast" quality of "red" and "black". What, exactly, tells you that one is above or below the other?
Price dictates that. It doesn't matter what kind of naming scheme you use, price is what ultimately determines whether someone makes a purchase. At best you can establish a strong brand that customers trust and then flog off mediocre hardware at high prices, but that speaks more to the power of brand. If you've got $300 to spend on a GPU, you look at GPUs that cost about $300, maybe a little above and below to see if you can get away with spending less or can get a really good deal for a little bit more, but price is the ultimate starting and ending point. You might know the names of some expensive products or brands that you lust after, but you ultimately buy in your price range, regardless of what that product is called.
The names are essentially meaningless. They only exist to differentiate the products or to serve as a label. If Vega Red Star X gets more eyeballs than Vega 590, then Vega Red Star is a better brand, especially if that extra attention translates to sales. Who cares if someone isn't sure whether Blue Star is better than Red Star, the price tag tells them that. Numbers just suggest a more natural ranking, but they become worthless when looking at generations. An R9 370 isn't a better GPU than an R9 290, so you still need to understand how that numbering system works instead of just looking at the raw number. However most customers probably wouldn't make that mistake, because a 290 costs more and unless that person is a complete plonker they'll probably start to realize that there's more to the numbering system than just thinking the bigger number is better.
Using colors isn't really any worse since the GPU number system is almost just as arbitrary. How would a normal person know that there's a dividing line between the R9 280 and R9 290 that's more significant than that between the R9 270 and R9 280? They're both just 10 apart, but really the gaps are far bigger than that. The only real reason to keep the existing system is because people are used to it, or at least people who talk about GPUs a lot are used to it. The x80 part means a certain thing in terms of AMD cards, but if you're just walking into the store, you don't have that domain knowledge and AMD Radeon RX 480 is as worthless to you as AMD Vega Blue Star. Neither conveys any particular meaning so you just end up looking at the price tag and working from there.