Back before development was started on POV-Ray 3.7.1, it was pointed out 
that poly_wave 2.2 can be used to achieve non-linear gradients with 
assumed_gamma 1.  Alas, while trying to adapt Warp's wood texture to 
linear color, I realized that poly_wave only gives the desired result 
for the very simplest of gradients.

The attached montage compares poly_wave 2.2 with blend modes 1 to 3, 
blend_gamma 2.2, for a variety of color maps on gradient x.  The color 
maps are, left to right, top to bottom:

   [0.0 Red] [1.0 Green]
   [0.0 Red] [1.0 Yellow]
   [0.0 Yellow] [1.0 Red]
   [0.0 Red] [1.0 Black]
   [0.0 Black] [1.0 Red]
   [0.5 Red] [1.0 Green]
   [0.0 Red] [0.5 Green]
   [0.5 Red] [1.0 Yellow]
   [0.0 Red] [0.5 Yellow]
   [0.5 Yellow] [1.0 Red]
   [0.0 Yellow] [0.5 Red]
   [0.5 Red] [1.0 Black]
   [0.0 Red] [0.5 Black]
   [0.5 Black] [1.0 Red]
   [0.0 Black] [0.5 Red]
   [1/3 Red] [2/3 Green]
   [1/3 Red] [2/3 Yellow]
   [1/3 Yellow] [2/3 Red]
   [1/3 Red] [2/3 Black]
   [1/3 Black] [2/3 Red]

The issue is that poly_wave does not adjust the colors themselves; it 
adjusts their positions within the gradient.  If you want traditional 
gamma 2.2 gradients without mathematically micromanaging the color map, 
you'll need to use POV-Ray 3.8.

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Download 'blend_v_poly-pbi.png' (15 KB)

Preview of image 'blend_v_poly-pbi.png'