GO:0097101

The process involved in the specification of identity of a blood vessel endothelial cell. Once specification has taken place, a cell will be committed to differentiate down a specific pathway if left in its normal environment. A blood vessel endothelial cell is an endothelial cell of the vascular tree, which includes blood vessels and lymphatic vessels. [CL:0002139, GOC:dgh, PMID:21521739]