Different style for allday / timed events
I would appreciate to see allday events as they are today but not allday events "lighter". The way Google handle it is good in my opinion. With many small meetings over the day it's very unobviously in the month view. If the calendar color is blue, allday events should be displayed white-on-blue and not allday events blue-on-white.
cc @jancborchardt
I like how fantastical does it:

Yeah ... perfect :-) Correct me if I am wrong, but it seem for me not so much work to realize. Could I support in any way to have it in the next release?
Send a pull request :P
@jancborchardt Mind taking a look? :)
For all day events I would use the current way (background color) and for non-allday we could color the text. That’s a simpler more direct indicator than what Fantastical does with the added dot – and actually Business Calendar 2 on Android does that.
If that ends up to be not readable, we can still check for other options.
but it seem for me not so much work to realize.
Thinking a bit about this I'm pretty sure this won't be done with some CSS magic. As far as I can tell right now we have to implement our own month view.