Matrix "B12" which converts linear RGB values (0-1) to a
"representative" reflectance curve (over wavelengths
380 to 730 nm, in 10 nm intervals).

See http://scottburns.us/reflectance-curves-from-srgb/
for more derivation and more information.

0.0933	-0.1729	1.0796
0.0933	-0.1728	1.0796
0.0932	-0.1725	1.0794
0.0927	-0.1710	1.0783
0.0910	-0.1654	1.0744
0.0854	-0.1469	1.0615
0.0723	-0.1031	1.0308
0.0487	-0.0223	0.9736
0.0147	0.0980	0.8873
-0.0264	0.2513	0.7751
-0.0693	0.4234	0.6459
-0.1080	0.5983	0.5097
-0.1374	0.7625	0.3749
-0.1517	0.9032	0.2486
-0.1437	1.0056	0.1381
-0.1080	1.0581	0.0499
-0.0424	1.0546	-0.0122
0.0501	0.9985	-0.0487
0.1641	0.8972	-0.0613
0.2912	0.7635	-0.0547
0.4217	0.6129	-0.0346
0.5455	0.4616	-0.0071
0.6545	0.3238	0.0217
0.7421	0.2105	0.0474
0.8064	0.1262	0.0675
0.8494	0.0692	0.0814
0.8765	0.0330	0.0905
0.8922	0.0121	0.0957
0.9007	0.0006	0.0987
0.9052	-0.0053	0.1002
0.9073	-0.0082	0.1009
0.9083	-0.0096	0.1012
0.9088	-0.0102	0.1014
0.9090	-0.0105	0.1015
0.9091	-0.0106	0.1015
0.9091	-0.0107	0.1015