Todo depende del color del cristal con que se mire
We use this expression to mean that there is not an exact beauty standard. What is beautiful for some is not for the others. We all have different likes and dislikes.
A beholder is a person who sees something or someone else. It is common that we, as beholders, emit a personal opinion after looking at something or someone else. When two people watch the same thing but they have different opinions about it, we simply say that the reason for this disagreement is that “Beauty is in the eye of the beholder.”