Hi,
I think this is a template issue, Calendar is build with bootstrap dropdown, seems that your template uses a dark background for dropdown but do not have any CSS rules for make light the links.

Please post me your site link (to keep it private you can use the form below the reply in "Site Details" tab). we will send you the CSS code to add in your template configuration

Done

Hi,
you should add following CSS code:

.jsndatepicker.dropdown-menu { background-color:white;border-color:#ccc; }

To add this code in purity III you have 2 different ways:
1. From Extensions->Templates->Purity III->Custom Code you can add style tag and put the code in parameter "before /head"
2. You can create a file called /templates/purity_iii/css/custom.css and put the code inside this file

Perfectly worked!
Thanks a lot!