Laurent polynomial approximation of the CIE 1931 chromaticity coordinates of the Planckian locus. Designed for the range 1000-20000 K. Here is the basic algorithm and coefficients assuming a 2° standard observer:
f(x, c) = (c[0] + x * (c[1] + x * (c[2] + x * (c[3] + x * (c[4] + x * (c[5] + x * c[6])))))) / (x * x * x)
cx = [4.60243e+08, -1.34958e+06, 1.49958e+03, 2.20742e-02, 1.86755e-05, -7.48912e-10, 1.12218e-14]
cy = [8.19188e-02, -1.32154e+00, 8.63682e+00, -2.95048e+01, 5.67579e+01, -5.42917e+01, 1.98083e+01]
x = f(t, cx) // t is temperature in kelvin
y = f(x, cy) // y reuses the x coordinate
Original data by Mitchell Charity:
http://www.vendian.org/mncharity/dir3/blackbody/UnstableURLs/bbr_color.html