I've seen literal translations like 穿紫色日 (wear purple day) or 穿紫色衣服日 (wear purple clothes day) but the most common and somewhat official translation seems to be 紫色纪念日 (purple commemoration day), so I would go with that.

<a href="https://www.glaad.org/files/SDResourceKit_cn.pdf" rel="noopener noreferrer" target="_blank">https://www.glaad.org/files/SDResourceKit_cn.pdf</a>;

<a href="https://baike.baidu.com/item/%E7%B4%AB%E8%89%B2%E7%BA%AA%E5%BF%B5%E6%97%A5" rel="noopener noreferrer" target="_blank">https://baike.baidu.com/item/%E7%B4%AB%E8%89%B2%E7%BA%AA%E5%BF%B5%E6%97%A5</a>;

多谢Miriam! That’s a great explanation, I really appreciate your time and effort.