when annealing metal, i look for a dull red color; it’s like a terra
cotta color, but a little pinker. i also turn off my lamp so i can
watch the metal better. for tubing, i’d use either a kiln or a very
soft flame to anneal.
you might try running wire through the tube to keep it from kinking
when you bend it. it would have to be fairly flexible to pull out
after bending the tube.
i hope i’ve helped you.