No friend, there's no reasons for that. I just pick any pictures that I think will suite my wrietup, but you are right, it seems I have always picked white pictures. Here is my next post after seeing your reply, I used a black picture. I will make sure to look for black pictures too.

https://steemit.com/steemiteducation/@focusnow/finding-your-orientation-the-10-most-important-human-values