Pretty but unusable
We use Google for our primary office calendaring app.
One of the nice features is that you can share your calendar with everyone in the office, allowing them to see at a glance when you’re free or busy without having to set up an invitation.
Everyone gets their own color.
So you can tell at a glance that the purple blocks on the calendar mean Charley’s booked all day. Or does it mean Lou is booked all day?
Well, at least your own calendar is a distinctive pink color. What do you mean, you can’t tell these two colors 
apart?
At least you’re not red-green colorblind (as approximately 10% of the male population is), because then you’d probably see no distinction between these colors: 
These colors are pretty. Clearly, someone went to some trouble to select colors that harmonize so well.
They just didn’t think of the purpose: color-coding is supposed to help you differentiate at a glance. Differentiation requires obvious, visible contrast.
But it could’ve been worse – these colors could’ve been used in a pie chart! That happened with a customer of mine a few years ago. Their designer just didn’t understand why I didn’t think the all-shades-of-light-green pie chart was a good idea…
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