Can't believe I just realized, but this GMK set doesn't have a pink on red sized 1x1 | \ (pipe,backslash) keycap. I'm so sad 
Yes it does. It's on the bottom right of the base kit.
That is RED on PINK (PINK COLORED keycap) not the PINK on RED ( RED COLORED keycap).
For more clarification if you look at the bottom left in row 2 there's a pipe | and backlash \ that is PINK on RED ( RED COLORED), but it's not 1x1 sized.
Some sets don't even include mod-colored tilde these days because it's "not a modifier key".
HHKB Split backspace is as follows. Note that pipe/backslash is second from the right on the top row:
The included mod colored tilde key allows 60% HHKB layouts look a bit more symmetrical, but mod-colored R1 1u pipe is not a key that is commonly used or asked for.
The latter won't be included in any future sets of mine, sorry if this is disappointing news.
