Baroness Tanni __-Thompson, Welsh athlete (4)

I believe the answer is:

grey

(Other definitions for grey that I've seen before include "Unclear (area); dull (weather)" , "11 - if of 10, white" , "White-haired - horse" , "Tom Pearce's horse" , "Dismal - colour" .)

I've seen this clue in The Guardian.

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