I bought these 80g packs of dehydrated blue pea (aka blue butterfly) flowers in a Thai grocery shop in Cabramatta for A$7.20 each. Let's see how the results compare for making Nasi Kerabu. My previous batch of Nasi Kerabu came out a grey colour using blue pea flower powder - it could be that the batch I was using was old but truthfully I've heard the same complaint from others who have had the same problem (ie. their kuihs turning out black) even using newer batches.
Tagging since you were asking about the powder!