English: The angle of maximum intensity is different for each color of light, creating the colors in the 22° halo.

The 22° minimum angle of deflection corresponds to a wavelength of 0.52 μm which is in the center of the green region of the visible spectrum. If however one considers the wavelength of peek sensitivity of the eye, which is 0.555μm, the minimum angle of deflection is at the angle of 21.9°. Red light however, which is at the far right of spectrum, in the illustration, has a lower index of refraction and so it is deflected by the smaller angle of 21.6°. The light at the blue or violet end of the spectrum is deflected by the larger 22.6° angle.

Created using the free open source program Inscape [1] and the free graphical program Graph [2].

It was created using the lower table of refractive indexes to create a 5th order polynomial approximation. That was then plugged into the equation...
Angle= 2*(60-ACOS(COS(60)*n))
which gives the minimum deflection. Note: Minimum deflection occurs when there is perfect symmetry between the incident and refracted ray. The final equation was... f(x)=2*(60-ACOS(COS(60*TR)*(-0.64433175*x^5+2.6695221*x^4-4.1981692*x^3+3.2308243*x^2-1.2612818*x+1.5139999))*TD) where TR=2pi/360 and TD=360/2pi

Source of the below index table is Optical constants of ice from the ultraviolet to the microwave. Warren and Brandt (2008)

Wavelength ________ Refr. Index
microns

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0.35 ______________ 1.32492
0.36 ______________ 1.32376
0.37 ______________ 1.32262
0.38 ______________ 1.32152
0.39 ______________ 1.32045
0.40 ______________ 1.31940
0.41 ______________ 1.31854
0.42 ______________ 1.31775
0.43 ______________ 1.31702
0.44 ______________ 1.31633
0.45 ______________ 1.31569
0.46 ______________ 1.31509
0.47 ______________ 1.31452
0.48 ______________ 1.31399
0.49 ______________ 1.31349
0.50 ______________ 1.31302
0.51 ______________ 1.31257
0.52 ______________ 1.31215
0.53 ______________ 1.31175
0.54 ______________ 1.31136
0.55 ______________ 1.31099
0.56 ______________ 1.31064
0.57 ______________ 1.31031
0.58 ______________ 1.30999
0.59 ______________ 1.30968
0.60 ______________ 1.30938
0.61 ______________ 1.30909
0.62 ______________ 1.30882
0.63 ______________ 1.30855
0.64 ______________ 1.30829
0.65 ______________ 1.30804
0.66 ______________ 1.30780
0.67 ______________ 1.30756
0.68 ______________ 1.30733
0.69 ______________ 1.30710

0.70 ______________ 1.30688