Nice techniques and I know I'm being pedantic here but those sheets are not Flemish Bond, they are Stretcher Bond. Flemish bond has alternate headers and stretchers on each course.

Just an observation, but, in real life, mortar was seldom actually white, coming in various shades of grey, brown or yellow, depending on the type of cement and sand being used, and sometimes deeply coloured, perhaps black, to suit the architect's whims.  There are only a couple of examples of white mortar I can think of. One is where Historic England or a client has demanded that lime mortar should be used, for authenticity, and this does start off white, but slowly mellows, and, when used for repairs, stands out starkly when compared with the, perhaps, hundred year old existing mortar, which may have darkened considerably over the years, particularly if the area was smoky prior to the Clean Air Act; sometimes the restorers will deliberately age the mortar to make it a better match.   The other is in tuck pointing.  This is a technique to make rough brickwork look superior, and can be seen in places like 10 Downing Street.  The façade is built using dark bricks, and the mortar is coloured to match and is flush pointed. After a short curing period a narrow routing tool, perhaps ¼ inch wide, is run along the centre line of the joint, using a straight edge or line, and the resultant groove filled with white lime putty. 

A few examples from my area. A Victorian terrace, with London stocks and red brick quoins and arches, with a creamy coloured mortar.

A more modern example - Elizabethan I suppose, with a a dark red brick and a darker shade of mortar.  What is interesting is the way the top half here, which is a balcony, shows the effect of weathering, with dark mould and white staining where chemicals have leached out of the modern mortar mix.  The lower section has been protected by the overhang of the balcony and shows very little weathering.

And finally, a wall on the house opposite the first example, where the end gable had been painted black, and has been subsequently repointed. Thanks to the contrast the new mortar does look very light, but it is a pale grey in colour.