Is there a way to change the orange colour of the "date" option?

Design Q; Is there a way to change the orange colour of the "date" option? 

Yes, it's possible. You can inject the CSS code below to change the highlighted orange box in the calendar field.

div.calendar tr.days td.today {

    font-weight: bold;

    color: #000000;

    background-color: #f6cdcd !important;

}

The color: #000000; attribute will change the font color:

And the background-color: #f6cdcd !important; attribute will affect the orange box color in my sample screenshot above.

I hope that helps. Let us know if you have any questions or if you need further assistance.