Individual Tint on 64+ instances sounds like recipe for killing graphics performance. especially if they start overlapping and especially on mobile. might be ok on desktop but you might be eating GPU performance that could be used elsewhere.
it would probably be better to still have just one object but bake the tints into animation frames and just set the frame to change the color.
However, i have learnt, asking performance questions, even to the experts, is mostly pointless.
The only way to really gauge how different approaches will affect performance for your specific requirements is to try it all yourself on your target machine.
Create a text box with CPU, FPS GPU time etc. create your 64-128 tinted instances / boxes and you should find out for yourself, in a few minutes, which is the better approach. And let us know your finding as I would be interested.