how to change the edit box color in gui?

i want to change the background color of my edit box after i clicked my push button.

what i did was

a=get(handles.edit1,'string');

if a=='2';

    set(handles.edit1,'BackgroundColor','red')
end
%these codes are under pushbutton1 callback function.

but still it doesnt change anything to my edit1 background.

what is wrong with it?

the command window doesnt say anything about any errors or mistakes111