// make the trail
function MakeTrails( entity, col )

 local trail = ents.Create( "env_spritetrail" )
  trail:SetPos( entity:GetPos() )
  trail:SetParent( entity )

  trail:SetKeyValue( "targetname", "" )
  trail:SetKeyValue( "parentname", "" )
  trail:SetKeyValue( "lifetime"  , "2.5" )
  trail:SetKeyValue( "startwidth", "3"   )
  trail:SetKeyValue( "endwidth"  , "1"   )
  trail:SetKeyValue( "spritename", "sprites/laserbeam.vmt" )
  trail:SetKeyValue( "renderamt", "255"  )
  trail:SetKeyValue( "rendermode", "5"   )
  trail:SetKeyValue( "rendercolor", col  )
  trail:Spawn()
end


// useage

function ENT:Initialize()
	MakeTrails( self.Entity, "50 100 255" )