It looks like the mortar has run down the face brickwork on the lower half of the house, or it could be salt coming out of the bricks, although I suspect it’s mortar staining, either way if it’s cleaned down with brick acid and jet washed it should clean up okay.
Just seen the other photos,
It’s definitely mortar on the bricks, it should clear up, for some reason there’s been bricks patched up and not very well either, they need the mortar grinding out and repointing with the correct sand, cement mix.
If you have concerns over the build can you ask the builder if you can have a look round while the build is in progress, if so take a spirit level with you and check all around the house that it’s level and plumb, check for any bulges in the walls especially around the points where the scaffold lifts have been, roughly around every 1.8 meters vertically, the windows have been fitted so the staircase should have been fitted, check the treads for creaking and that the newal posts are plumb.
Unfortunately it’s pot luck as to the tradesmen that are working on it, not all of them care about their standard of work, nowadays most trades are run by “barrons” who don’t always supervise like they should and the site managers don’t inspect like they did 20 years ago, again some are pretty inept at their jobs and haven’t risen through the trade, so don’t always know what to look out for, their often too busy drinking coffee and talking to their mates on the phone, sad but true.