Add ability to add background color to AppWithinMinutes-fields

Wouldn't it be useful if a creator of an AppWithinMinutes could decide the background color of a field. Sometimes it feels convenient if I could highlight fields visually by adding a certain color to them. I would prefer to be able to do it myself when creating the field instead of asking somebody else to change the CSS.

I don't claim to be knowledgeable about XWiki or programming so I don't know if this is a reasonable request or not.