Color by expression and variable

[japhias]

Dear all,

I have dashboard with a collection of pictures. In an extension I can visualize a preview of one picture by following expression:

=subfield(concat(image_name,';'),';',imagePreviewId)

With two buttons I can increase and decrease the imagePreviewId to scroll through the pictures.

The pictures are geo tagged, so that you can see the position on the map widget. There I want to color the image that is previewed in the extension by this code:

=if(image_name=subfield(concat(image_name,';'),';',imagePreviewId),'green','white')

Unfortunatley this is not working: If the imagePreviewId is 1 all points are green, does it have another value then all points are white.

Someone an idea for an adjustment?