*quoted and placed here for further investigation*
I imagine William could be the son of a couple who married 27 Aug 1758 in
Bristol, St James - William PERRY and Elizabeth
COLSTON (the original records obviously need checking because of the surname discrepancy)
There are two marriages on the BVRI for a William
PARRY to a Mary - one to a Mary
BURGESS (St James 15 Jul 1781), the other to a Mary WOODEFIELD (St Philip and St Jacob 22 May 1783). But, since neither show the
COLSTON middle name, they might not be relevant. William
COLSTON PARRY and Mary first have children christened 25 Feb 1787, but there are three children on the same day, so it's likely two are not babies.
Adam