I think Yamaha have a range of designs they're happy with and simply changing them for a difference between this year and last, especially just finishes a la Fender, isn't worth it to them. They make so many different instruments they need to be rational about what will actually sell. For a trad looking bass like the BBs, white, black, blue, TS will sell consistently whereas sparkle pink, or even just a bright yellow will sell far less. I think the caramel TRBX605 is really pretty, but it's not 'traditional' and that alone would put off some buyer (just talking colour here).
Yamaha's pianos and AGs are great (own / owned both), they are a known quantity and consistent and why change them?