Can't put gradient onto both sides of face

Untitled.skp (5.9 MB)

I used Gradientator to give this plane of mine a gradient color. But it put color on the wrong side. I kept trying to select the surface and applied the colors on the desired side (which is the white one, and not the colored one), but I keep failing.

The gradient color is applied to the ‘front’ of the surface [View > Monochrome to see this]
The surface actually consists of 617 faces [temporarily use View > Hidden Geometry > On to see this]
If you want the color to also be on the faces’ ‘back’, then select the colored surface > right-click > context-menu > Reverse face. It flips all of the faces in the surface, keeping the color in tact…
Now redo the gradient color on the ‘front’ of the surface…
Both sides of the surface should now be colored as you hope ?
If you want one side to be ‘blank’ repaint it as needed…

Thank you very much!
It is now fixed!