The current client behavior allows players to set the color of their outbound text that other players will see. Your proposal of using color would still be susceptible to spoofing. (And before someone suggests it, I'd rather not see that ability taken away, as it does have its legitimate uses. )
Also, randomly dropping loot into a group member's inventory seems like a very disruptive change to an otherwise functioning system. The bottom line is: you need to trust your group members to do the right thing (whatever 'the right thing' may be). Changing the looting process to some sort of automatic distribution will not change that bottom line.
We'll likely end up having to change the messaging protocol for /emote (and possibly other channels) so that players cannot send anonymous text.