What exactly are you trying to do? Do you want to change the colour of the text in the search field, or do you only want to change the colour of the default text?
Technically, both are possible. (Assuming you want to change the colour in the HTML5 layout.) For all text:
For the input field with a specific text:
Note that the value must be an exact match. Also, it will not work on IE7 or earlier.
this is the formatting of the default text (e.g. "-Search-") I want to
change. The text itself can be changed in ther LNG file but I have not
found a way to change its formatting in the compiled app.
Note that the colors appear as I want in the preview and when I view the
HTML5 output in the browser. But after installing the app generated by
Robohelp, the text is always displayed in a dull grey. So possibly this
is a feature of the andoid SDK or whatever and cannot be changed at all?
To my knowledge, the Android output uses the phone's default browser engine to render the page. You can modify the CSS "input.wSearchField" to change the appearance of the default text size, color, orientation, etc.
color: green !important;
Into your mobile.css file.