Most white, former monarch looks tense (7)

I believe the answer is:

greyest

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'most white' is the definition.
Both the answer and definition are superlative adjectives. Maybe they are linked in a way I don't understand?

'former monarch looks tense' is the wordplay.
'former monarch' becomes 'GR' (short for Georgius Rex, King George in Latin).
'looks' becomes 'eyes' (eyeing is a kind of looking).
'tense' becomes 't' (grammatical abbreviation).
'gr'+'eyes'+'t'='GREYEST'

Can you help me to learn more?

(Another definition for greyest that I've seen is " most dull".)

I've seen this clue in The Independent.

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