Enables pseudo-transparency for the popup-menu. Valid values are in the range of 0 for fully opaque popupmenu (disabled) to 100 for fully transparent background. Values between 0-30 are typically most useful.

It is possible to override the level for individual highlights within the popupmenu using highlight-blend. For instance, to enable transparency but force the current selected element to be fully opaque:

:set pumblend=15
:hi PmenuSel blend=0

UI-dependent. Works best with RGB colors. 'termguicolors'

(default 0)