Ghata (Hari Ghata / Shyam Ghata)
What it is
Ghata is the name of a seasonal shringar (adornment) tradition in Pushtimarg: a distinct jewelled headpiece and ornament set, still made by Nathdwara's shringar craftsmen today, that marks a shift in how Shrinathji is adorned through the colder months. "Hari Ghata" and "Shyam Ghata" name two points within that same seasonal tradition, appearing on the calendar as the season turns from Kartik toward the depth of winter.
Pushtimarg shringar changes constantly through the year with the season and the utsav being kept, mostly through the Mastak (head) adornment, and Ghata is one thread of that much larger, centuries-old wardrobe.
Why we observe it
Shringar in Pushtimarg is never decoration for its own sake: dressing Shrinathji for the season is treated as literal, attentive seva of a living person who feels the cold the way anyone does, adorned accordingly rather than left in clothing suited to a different month. Ghata marking the calendar's turn into the cold season is one more instance of the sampradaya's insistence that seva follow real time and real weather, not an abstract, unchanging ritual calendar.
A Vaishnav does not need to know every detail of the ornament to take the bhav from the day: attentiveness to Prabhu's comfort, expressed through something as concrete as what He is dressed in, is itself a form of love.