I'm sorry: I completely misunderstood your question..
I tried this workaround (but it doesn't solve anything): I set to a random value an instance variable called "B" for the Blue object. Then I assigned the B value for the tint FX but while the B variable value was different for each Blue object, the tint was always the same.
I think the reason is because Tint is specific for the object itself (read "global"). So even if an instance variable could be different for every Object, an effect defined as an FX of the Object can be only global..
I hope you can solve this issue.
let me know, because I'm interesting in this argument (now I manage colors with the frozen animation workaround...)