Today what I've successfully done is I can change the color of default selected value in select box with jQueryMobile. Frankly, this feature is missing in jQueryMobile because nobody can obviously know whether any value is selected in select box or not. Because they missed out to let users know about it. That's why I need to add the customize function of myself.
selectedIndex = select.selectedIndex == -1 ? 0 : select.selectedIndex,
Then, we need to add the following customize coding after that,
className = select.selectedIndex == 0 ? "" : "ui-select-active",
(I've already showed the characteristic of above class name in my previous post. READ HERE.)
After adding above coding, we need to search the following coding. I think, it will be located after 7 lines of above coding.
.text( $( select.options.item( selectedIndex ) ).text())
Once you found it, we need to add the following coding after that.
.addClass( className )
After adding successfully, save it and rendering it. So, you can changed the default selected value in select box at jQueryMobile.