P2 selects how the terminal draws the background color.
P2 Meaning
0 or 2 (default) Pixel positions specified as 0 are set to the
current background color.
1 Pixel positions specified as 0 remain at their
current color.
Both modes are now supported.
Ref. https://www.vt100.net/docs/vt3xx-gp/chapter14.html