I'm under the impression that the part numbers are agnostic as to which colours they can be, although at some point retailers were distinguishing between 1395900 'WHITE' vs 'BLACK'.
I took a quick look at the HMM for some random PS/1s and couldn't find anything that differentiates colours, I like the opening logo (some PS/1s BIOSes had that as a splash screen):

1 1395900 1 - U.S.
1 1395900 1 - Australia, Bangladesh, Brunei, China, Hong Kong, Indonesia, Macau, Malaysia, Myanmar, New Zealand, Philippines, Singapore, South Africa, Sri Lanka, Thailand
1 1396497 1 - Arabic countries
1 1395910 1 - Belgium (Dutch)
1 1395908 1 - Belgium (French)
1 1399045 1 - Brazil
1 1399358 1 - Bulgaria (Cyrillic)
1 1395900 1 - Canada (English)
1 1395901 1 - Canada (French)
1 1399377 1 - Czech Republic
1 1395916 1 - Denmark
1 1395913 1 - Finland
1 93F0114 1 - France
1 1395907 1 - Germany
1 1399078 1 - Greece
1 1399379 1 - Hungary
1 1395919 1 - Israel
1 1395912 1 - Italy
1 1397036 1 - Latin America (Spanish)
1 1395909 1 - Netherlands
1 1395914 1 - Norway
1 1399376 1 - Poland
1 1395915 1 - Portugal
1 1399380 1 - Romania
1 1399375 1 - Russia (Cyrillic)
1 1399374 1 - Serbia (Cyrillic)
1 1399378 1 - Slovakia
1 1395920 1 - Spain
1 1395913 1 - Sweden
1 1395921 1 - Switzerland (French)
1 1395922 1 - Switzerland (German)
1 1395912 1 - Switzerland (Italian)
1 1395917 1 - Turkey
1 1395906 1 - UK/Ireland
1 1399081 1 - Yugoslavia (Latin)
---
I think it's probably
too late to hunt some of this stuff down since it's all long gone and recycled, we'll need a time machine. And black PS/1 setups weren't common to begin with; I wonder if their keyboard were even sold separately or only exclusively bundled with a system.
Sadly, it is looking like they were only ever bundled and not sold individually--which would explain their obscurity.