How to quickly invert the color of a texture

 (by Jean-Sebastien Perron)

1-Add an "Operation" operator below the desired channel (in this case the texture color).

2-Select type "1-P1"

3-Make the output and input of the "Operator" to the same as the desired channel (in this case the color channel).

Note : You can invert the color or the result of any channel that way.