How to change the colors of labels in booking form?

This customization is only for the Booking Calendar Free version. In the paid versions, you can easily configure booking form fields and their style at the advanced form configuration at the Booking > Settings > Fields page.

1) Please open this file ../wp-content/plugins/{Booking Calendar Folder}/css/client.css
and add to the bottom of that file this code:

.booking_form .control-label {
  color: #FFF;

Of course instead of white color #FFF you can set some other.

2) In the same way possible to change the color of text inside of the text fields, text-area elements and selectboxes. You need to add to the bottom of this file ../wp-content/plugins/{Booking Calendar Folder}/css/client.css this code:

.booking_form_div select,
.booking_form_div textarea,
.booking_form_div input[type="text"] {
  color: #FFF;

Again instead of white color #FFF you can set some other color.

Important! Please note after update of plugin to the newer version update, you will be need to make this fix again, because all Booking Calendar files will be overwritten.

How to edit plugin file in WordPress 4.9 or newer