Question

I'm having problems converting some colours from sRGB to Munsell. I'm no expert in this field so can well believe I'm doing something daft but I don't know what.

I have a spreadsheet (2547 rows) of the main Munsell colours with their sRGB equivalents (I think this came via Paul Centore's work; the numbers check back to this anyway). I've written routine to convert sRGB to Munsell & have been using this spreadsheet to check my results.

Code:
import colour
import numpy as np
rgb = np.array([141,116,121])
XYZ = colour.sRGB_to_XYZ(rgb / 255)
xyY = colour.XYZ_to_xyY(XYZ)
munsell = colour.xyY_to_munsell_colour(xyY, chroma_decimals=1)

Issues:

1. I have about 55 Assertation errors e.g.
   Most of the colours here seem to be relatively low value & chroma but not all
   e.g. 02.5RP-9-02 RGB(241,222,239)
   AssertionError: ""array([ 3.08954081, 9.02276054, 1.84797444, 8. ])"" specification chroma must be normalised to domain [2, 50]!
   The 4th argument looks v strange to me & all cases have this format i.e. n.spaces.

2. I'm getting quite a lot of hue discrepances in those areas where one hue family changes to another.
   e.g.

10.0R -7-08 RGB( 242,150,128) my result: 0.1YR 7.0/8.0
10.0R -7-10 RGB( 254,144,114) my result: 0.1YR 7.0/9.9
10.0R -7-12 RGB( 255,136,97) my result: 0.6YR 6.8/11.0

I most cases, the sub-hue group in my result is < 1 rather than 10.0.

Can anyone advise me?