Add some irregular flat black splotches of the same brand of paint and your cucumber, I mean, rifle will look fine. I'd be putting a bit of flat black spray paint at an angle, lengthwise, on the handguard and forestock. And a smallish patch on either side of the receiver. On the top of the buttstock just aft of the grip.
The purpose of camouflage is to break up the shape. A bit of black on that shade of green will do it.
Be sure and sand it a bit so the next colour will stick.