hips won't dissolve in acetone - you need limonene. Yeah the same stuff that's supposed to repel mosquitos.

Pva and warm water are your best bets.

And yes a filaments colour does effect how it prints.

support material isn't there to hold weight, it's mainly there to support plastic until it sets - at which point there is no weight bearing down on the support.
It's certainly not 'spongey' - fairly flexible maybe, but that's not an issue.