The "inversion" is not working.
I do laboratory work on the subject of "Computer Graphics".
I reach this point: "3 14. Hold Ctrl and click the Shade layer, invert the selection Select → Invert or (Ctrl + Shift + I), delete the selected part of the gradient key Delete Deselect (Select → or deselect (Ctrl + D). ". And the inversion button is not active. What should I do?
Win 8. Trial version of the program.

