SELECT DISTINCT
  CASE f WHEN 1 THEN ProductColour END AS ProductColour
  CASE f WHEN 2 THEN ProductSize   END AS ProductSize
FROM shoptransfer s
  CROSS JOIN (SELECT 1 UNION ALL SELECT 2) x (f)

SELECT DISTINCT
  CASE x.f WHEN 1 THEN s.ProductColour END AS ProductColour
  CASE x.f WHEN 2 THEN s.ProductSize   END AS ProductSize
FROM shoptransfer s
  CROSS JOIN (SELECT 1 UNION ALL SELECT 2) x (f)

This produces the same output as Brian's solution. The idea is to make every row of shoptransfer output twice without scanning the table twice. That is achieved by cross-joining the table to a tiny tally table created 'on the fly'. When the tally table's first row is current, the query produces a row with a ProductColour value and NULL as ProductSize, and the second time it's the other way round, i.e. ProductColour is NULL and ProductSize contains a value from the shoptransfer table.

The syntax used for defining the tally table may seem a bit unusual. For those of you not acquainted with that way of aliasing, x is the subselect's alias, the f in brackets is the alias for the subselect's single column. In short, the following two definitions are absolutely equivalent to each other:

1. (SELECT 1 UNION ALL SELECT 2) x (f)

2. (SELECT 1 AS f UNION ALL SELECT 2) x