mathmos does offer to make custom bottles but its expensive and white does always become yellowish very quickly. I have very rarely seen a true white which lasted.
I use a astro base (matt silver form the 90s I think) with a heritage clear and turquise bottle. It over heats in about 3 to 4 hours with a 40w spot bulb, but it work perfectly with a 30w spot bulb and doesnt overheat even if you leave it on all night. Its take 2 hours exactly to start flowing.
The new chrome Astro uses a 35w halogen lamp. The old astro uses a 40w halogen lamp. if you put a 40w halogen lamp in the heritage bases with a normal (non heritage) bottle it will flow correctly. The heritage bases take more heat than the regular bases, so they make the fluid different to compensate. Just use a hotter bulb.