Do we have to let go the "Subha Sanna" completely? Lord Buddha said that we should practise Asubha sanna (perception of the non-beautiful). Does it mean that we have to let go Subha sanna (perception of the beautiful) completely ? Are there anything that is Subha in this world?
As I know, The world is a Asubha thing. We can not find any subha thing in this world at all. So anything that is not related to the world is Subha. Buddha, Dhamma and Sangha help us to get rid of this world. That means they are Subha things. The conclusion is that we shouldn't have any Subha sanna towards anything other than Triple jems. Am I right?
The word subhasaññānuvattinī occurs exactly once in the five Nikayas and it warns of a danger:

Thig5.3:1.1: Due to improper attention,  I was racked by desire for pleasures of the senses.  I was restless in the past, lacking control over my mind.  Overcome by corruptions, pursuing perceptions of the beautiful, I gained no peace of mind.  Under the sway of lustful thoughts,  thin, pale, and wan, for seven years I wandered, full of pain,

Perceptions of the beautiful should not be confused with the third liberation:

AN8.66:3.1: Subhanteva adhimutto hoti.

AN8.66:3.1: They’re focused only on beauty.

The third liberation results from the heart's release by love.

SN46.54:12.9: The apex of the heart’s release by love is the beautiful, I say, for a mendicant who has not penetrated to a higher freedom.

The heart's release by love is mettācetovimutti, it is not the heart's release by the perception of beauty.
So although the Triple Gem is certainly beautiful, we should have proper attention towards the Triple Gem instead of merely perceiving them as beautiful.

AN2.126:1.1: “There are two conditions for the arising of right view. What two?  The words of another and proper attention.