This selection improvement feature is hidden behind the advanced
configuration key "PcbSelectionVisibilityRatio". It is turned off (1.0)
by default. Value values are from 0.0 to less that 1.0. From testing,
using a value between 0.1 and 0.3 produces the best results.
This fix uses normal alpha blending described in the link below. The
current design only uses the alpha of the object's color. It could be
improved by doing a full color alpha blending but using the color alpha
alone seems to result in satisfactory results.
https://en.wikipedia.org/wiki/Alpha_compositing
Fixes https://gitlab.com/kicad/code/kicad/-/issues/16126
Wayne Stambaugh