I think you're right that the females might prefer an opaque laybox, but then there's the problem of checking on them. In a transparent laybox, I can see without moving the bin whether they've laid, how much progress they've made once they've started, etc. If I gave them opaque layboxes, I'd have to pull out the bins to check on them, which would disturb them more. I am really loathe to disturb my females at any point during laying, even just by pulling out their bins, so my preference is to use transparent layboxes.