The Saxons system was to use a particular facing colour for two regiments and to give one regiment yellow buttons and the other one white. But in the case of the facing colour, pale blue, three regiments used this. In the early period this did not matter as Kurprincessen was a grenadier regiment and all its ranks wore the mitre (white buttons) and it was easily distinguishable from
Prinz Gotha Regiment, which also had white buttons, but whose rankers all wore the tricorne.
But between 1757 and 1761 Kurprincessen all were forced to wear the tricorne (the mitres had been lost at Pirna), and then later in 1761 they were all given lapels on their coats and bearskins. This created a problem distinguishing grenadiers of Kurpincessen with those of Prinz Gotha. The Saxon solution (in 1761) was to give the grenadiers of Kurpincessen medium blue lapels and waistcoat while retaining pale blue cuffs and turnbacks. Confused, I'm not surprised!