By default the "partially booked dates" (its means bookings for specific time-slot and available in Booking Calendar Business Medium or higher versions) is showing with small calendar icon at the bottom right side in each specific day cell, where exist bookings for specific time-slot. Because such bookings for time-slots can have pending or approved status, system also change background color for such dates.
Such workflow can be confused for some customers and sometimes need to show only calendar icon, but leave background color for such dates the same as for available dates. For having such view, you will be need to make some small fix in your calendar skin.

1) First of all, please check what calendar skin is active in your system. You can check it at the Booking > Settings General page in Calendar section. Please note, you calendar skin can be located at ../{Booking Calendar Folder}/css/skins/ or at ../{Booking Calendar Folder}/inc/skins/

2) Because you will be need to make fix, probably you need to create your own calendar skin in specific separate folder ( /wp-content/uploads/wpbc_skins/ ), its will save your customization during future updates of plugin. Please check how todo this here.

3) You will be need to add to the bottom of your calendar skin the CSS code for redefinition background color and text folor for such days.
For example for the "Premium Marine" calendar skin, this color can look like this:

.block_hints .block_time,
.datepick-inline .timespartly {
    background-color: #789;
}
.datepick-inline .timespartly.date_available a{
    color:#fff;
    font-weight: 600;
    text-shadow: 0 -1px 0 #333;
}

For other calendar skins, there will be different colors. In any way you can check what color you need to set there by checking section

/* A V A I L A B L E - BACKGROUND */

and

/* A V A I L A B L E  - Text A */

in your active calendar skin.

After saving your calendar, skin (if you was creating your own calendar skin), please open the Booking > Settings General page and select for "Calendar Skin" your new calendar skin file. Then save changes.

Please do not forget to clear browser cache before testing these changes.