You may need the latest Time.ly release of the FREE PREMIUM EDITION to change the CSS.
In the file calendar.css in wp-content/themes-ai1ec/umbra (or whatever theme you are using)/css/
Easiest way to find the code is to search (Ctrl + F keys on keyboard) for “poster”
change the filter: alpha(opacity=7);
to filter: alpha(opacity=50);
.ai1ec-posterboard-view .ai1ec-date-block-wrap . . . → Read More: All In One Event Calendar IE7 and IE8 Poster board view Date and Month Opacity Fix
