Originated July 21, 2018, when
BTS member V posted on WEIBO:
"紫爱你💜" which directly translates to
"I purple love you" or simply "I purple you" from Mandarin. The phrase orginally comes as "只愛你" which means "I only love you", but V replaced 只 (only) with the similarlly sounding 紫 (purple).
The wordplay is seen to be adamantly remarkable, considering even many
chinese-speaking fans did not notice the
pun at first, and V is a non-native speaker in English and Mandarin, both languages which of are necessary to make/understand this pun.
Because of this, the phrase "I Purple You" has now been popularized and is even used outside of
BTS and their fans.
V further defines Purple to be the color of trust and
long-lasting love, because Purple comes last in the rainbow, following all other colors.
In
short, "I Purple You" is slang for "I trust you", "I love you" and "I
will stay by your side".