Hi,
Well, this might be possible with a custom script code. I have constructed a small custom code snippet, and placed it into the functions.php file in your child theme directory. This should hide the child checkboxes until they are checked. For reference, here is the custom code:
Please note that I cannot guarantee this is going to work with every single case, but it should do the trick in most of them.
Coloring the checkbox background could be possible via custom CSS. For example this will color the background of the category id = 1 to red:
[code]label[for$=termset_1] {
background-color: red !important;
background-image: none !important;
}[/code]
You can use this as a template to create as many different colorings as you need.
I hope this helps!