I was looking in Feedback and found this case:
64812 - WebDatePicker greys out valid dates
It may be closed as designed because the Bootstrap Datepicker code that is used for this shows the same gray for previous/next month days and disabled days.
What is the problem? see this calendar and can you identify which days can’t be selected?

We need to hover over the days to see if the cursor and background changes to know if we can select the days from previous/next month days. Not easy to identify, but how about we change the color for disabled days? I think this is easier for the user:

To make the above change we just need to add this code to HTML Header <style> </style> code:
.datepicker table tr td.disabled, .datepicker table tr td.disabled:hover {
color: #d69696;
}
Some people may prefer to not show previous/next month days at all, we can do that with some CSS too and get this:

that way the user will need to move to April or June to select one of the few days available for those months:

we can do that with this code:
.datepicker table tr td.new, .datepicker table tr td.old {
height: 0;
line-height: 0;
visibility: hidden;
}
We can combine the two if we want. We can combine colors to make it clear that we can select anything in black and the red are not available, like this:

not using the gray color anymore.
Hope this helps.