I'm trying to wrap my head around the Open Assets specification that CoinPrism is using. If I understand it correctly, unlike OBC or POBC ways of doing colored coins, it seems the Bitcoin transaction rules do not actually help do any validation of the transactions. If I have 100 WTK, I can create a transaction which sends 200 WTK and the Bitcoin network will process that just fine, and it would be up to the colored coin software to determine that was invalid, right?
So in the case above, what are the rules about that transaction? Is it just ruled completely invalid? Can I then re-send a transaction for 50 WTK since the previous send will be deemed invalid?
OBC and POBC don't rely on the Bitcoin transaction rules either to verify transactions: the Bitcoin protocol has no knowledge of colors, so it's not possible to rely on that.
If you make an invalid transaction, depending on how inputs and outputs are setup, you may uncolor some or all of the coins you are transferring. If that is the case, they cannot be spent again (they have been uncolored, and no longer exist).
If there was such a thing as a color-aware client and miners were running it, it could reject such transactions.
You can check the example at the bottom of the document, it walks though the coloring process.