For those curious on changing the color of the select field text, "Select Industry..." in this example, I was able to change the color using this custom CSS:
.mktoForm select.mktoField {color: #999999 !important;}
The only slight issue, is that it changes the color for all the values... the "Select Industry..." default text as well as all the values you can select from the list.
If anyone knows of a way to change only the color of "Select Industry..." and not the values in the list, I would love to know how! I'd like to change the default 'select' text to grey, but leave all the values as black.