The other John Walker...

The death is announced of John Walker, the well-known coloured football player residing in Leith. He was better known as “Darkey” Walker, and is believed to have been the only professional football player of colour in Scotland. Walker, on joining Leith Athletic three years ago, gave promise of developing into a class player, his tricky play and dashing runs establishing him a warm favourite. The Heart of Midlothian entered into negotiations for his transfer, which was effected for the sum of £50. After playing for the Hearts for a season, the Tynecastle club gave Walker his papers, and at the beginning of last season he joined Lincoln City. He did not remain long with the English club, and returned home six months ago in ill-health. Consumption was the cause of death.
The Dundee Courier, (07.08.1900)

John Walker was the first black professional footballer in Scotland, and the first black professional to play in both the Scottish League and the Football League. His appearance in first class football was brief. He was an outside left noted for his pace and ball skill.

In 1898 he joined Leith Athletic from Leith Primrose.
Later that year he joined Heart of Midlothian.
Here is John Walker's record for Hearts. 3 league matches, no goals:

29.10.98 Hibernian (a) w 1-5
05.11.98 St Bernard's (h) w 3-1
12.11.98  Third Lanark (h) w 2-1

There is some speculation over whether Lincoln thought they had signed  the Scottish international John Walker, a Hearts team mate, rather than John 'Darkey' Walker. 
Walker's career with Lincoln was unspectacular. 6 Division 2 matches. No goals:

02.09.99 Middlesbrough (h) w 3-0
09.09.99 Chesterfield (a) d 2-2
07.10.99 Newton Heath (a) l 1-0
14.10.99 The Wednesday (h) l 1-2
04.11.99 New Brighton Tower (h) d 0-0
11.11.99 Grimsby Town (a) l 5-2

On leaving Lincoln Walker, who was having problems with his health, returned to Leith. Walker was 22 when he died, either of tuberculosis or pneumonia, in August 1900.

Looking for evidence about Walker, particularly his origins, I found that other on-line historians had not been able to establish many facts. There was speculation over his  birthplace. Leith was a port, and ports were more likely to have black inhabitants in Victorian Britain than other areas. One lead I did find online was that John's parents' names were John and Sarah.
According to the 1891 census (accessed via ancestry.com)  there were a John and Sarah Walker living at 8, Cable Wynd, Leith. They had 2 sons, the elder being John (b 1877).
John Walker senior's place of birth is given as 'Naturalvjed, Spain' (I took this to represent 'naturalized'). 
Moving back in time to the 1881 census, John Walker senior is identified as a Dock Labourer and his place of birth as India, West (!)- surely the West Indies.
It doesn't require a great leap of the imagination to come up with Port of Spain. This is pure speculation on my part. One thing that these census records do tell us , however, is that John Walker junior was born in Leith.