I'm working on the assumption that you've done something
to optimize your monk's flurry. That is, admitedly, an assumption. Possible avenues in heroic are somewhat limited, but by paragon you've got Werecheese, Lyrandar Wind-rider, Malec-Keth, Radiant Fist & Pelor's Boon in team Radiant Mafia, Blightbeast, Shocking Flame and some I'm sure I've missed. (page maintained here
Given that assumption, whatever you're using to juice your monk's flurry will juice the 2nd tap of Burning Brand
Yes, that might just be "Blistering Flourish
", which only works for Cha-secondary monks. But it's also anything else that applies to your flurry. Since, even if your focus is AoE striking, you still want to get as much as possible out of your flurry.
Edit: that does raise a fair point: By assuming you've juiced your flurry, I'm also basically assuming either past-paragon, or SFW-nova builds. Which would argue for a split rating Black/Sky Blue, with the text explaining that if you have some way of juicing your flurry, including Desert Wind, then it's sky blue. Otherwise consider it black, and retrain bait later in your career.
Also: the later Desert Wind powers don't apply the bonus damage as quickly: they're usually "creature ends turn in aura". That's simply not the same thing. So I'd tend to suggest that Burning Brand
is a power you keep forever/retrain into in paragon and never let go.