As @Marc Stridgen explained above, there are areas where opacity is indeed used. In this case, the opacity is used on the forum icons to indicate that there are no unread topics in that forum. If there are unread topics, the icon will appear darker. Take a look at how it looks on this community:
This is really easy to change, and requires only one small change to your theme. Edit your theme and add the following snippet to the file custom.css:
.ipsItemStatus.ipsItemStatus_read {
opacity: 1;
}
Note that this will make it hard to see if there are unread topics in a forum or not, so you should consider not making the icons for read and unread forums the same.