You don't have to "Find" the div after the page has loaded, you can do this as it is getting bound. I imagine that when you say "if it's checked" that you refer to the imagebutton acting as a checkbox, and you want to change the color depending on the location(path) of the image. So I would this in the div:
<div style='<%# doColor(Eval("ImageUrl")) %>'>
Content in the div
</div>
and then this in the code behind:
Public Function doColor(img As Object) As String
If img.ToString() = "MyPath" Then
Return "background-color:red"
Else
Return "background-color:green"
End If
End Function
that way if the ImageUrl equals "MyPath" the background of your div will be red, otherwise it will be green.