You can find this filter through
->->
This filter inverts Value (luminosity) of the active layer or
selection. Hue and Saturation will not be affected, although the
color will sometimes be slightly different because of round-off
error. If you want to invert Hue and Saturation also, use
->->.
Note that hue and saturation can be distorted quite a bit when
applying twice this filter for colors with a high luminosity ( for
instance, HSV 102°,100%, 98%, a bright green, gives HSV 96°, 100%, 2%
after a first application of the filter , and 96°, 100%, 98% after a
second application) . Thus, you should not expect to be able to apply
this filter twice in a row and get back the image you started with.