What could be the cause of powdery white pool water with a blue tint so thick you can't see the first stair along with residue on pool walls in a brand new gray plaster pool 2 days after tech visit?

Since you had a colored plaster, you are seeing the mortar hazing on the walls and floor over the darker aggregate. You are supposed to wash the pool with a mild acid solution to help to reduce this effect with colored plasters. The good news is that this condition will continue to fix itself as the pool ages. As a pool contractor I am very conscious to inform clients that this will occur with colored plasters often taking up to a year to be haze free. You could potentially acid wash with a stronger dilution however this will remove too much mortar and begin the pitting and roughening of the plaster prematurely.