Interpolate the R and B numbers logarithmically. We perceive light intensity that way, not linearly. For example, the same scene taken at a sequence of decreasing f-stops with everything else held constant yields a sequence of pictures that look successively lighter, with each step feeling roughly constant. However, the actual amount of light will go in a power of 2 sequence.

To interpolate a light level from A to B, you want to find a ratio, as opposed to a increment, that gets you there in the number of steps you want. In regular linear interpolation, if you wanted to go from A to B in 4 steps, you'd add (B-A)/4 each step. In logarithmic interpolation you want to multiply by some value each step. In this example, that multiple would be (B/A)1/4, which is the fourth root of B/A. In general, the mutiply factor each step is (B/A)1/steps.

For example, if you want to go from 5 to 39 in 4 steps, then each step must be (39/5)1/4 = 1.6712. The sequence would be:

 5.000
 8.356
13.964
23.337
39.000

Perform this interpolation on each of the red and blue values separately, assuming the green values are all normalized to 1 as you stated in your question.