Jono,
I have had a look, using LC Designer ES it is possible to set the colour of the value portion of the view to grey by accessing the Object / Field / Appearance / Custom and setting the background fill to solid (and picking a colour).
If you are using an earlier version, then setting the background to white (which might set the whole field to white). Then in the initialise event:
var fld;
fld = xfa.resolveNode("form1.p1.numericField1.ui.#numericEdit.border.fill.color");
fld.value = "192,192,192";
It appears that you can access the fill colour using the .ui appraoch, note that you need to correct notation for the field you are using, for example:
Date field = .ui.#dateTimeEdit
Dropdown = .ui.#choiceList
Checkbox = .ui#checkButton
Text field = .ui#textEdit
Numeric field = .ui.#numericEdit
Note that if the field does not have a background colour (i.e. at least white) then the script will not work.
Hope that helps,
Niall