Unusual in general or unusual in Germany? If you mean the latter, then it is definitely not the case. The trim of the insignia were issued in many different colours corresponding to the troop type (they are sometimes referred by its German name, Waffenfarbe, lit. troop colour). Light pink (rose pink) was assigned to armoured units, largely due to its association with motorized transport troops in Reichsheer, where it has been used between 1921 and 1935 (mosy likely as the one of the few colours that were still left unused and thus were assigned for the brand-new type of troops). The troop colours in Waffen-SS included the salmon-pink used by transport and rose-pink, as the one present on the photo, for armoured troops. Such a choice was nowehre close to strange, given that SD (security service and intelligence) used turquoise, signal corps used bright yellow and military police (field gerndarmes) used orange. These colours were also largely mirrored in Land Army (Heer). Air forces (Luftwaffe) also used rose-pink piping, although it was assigned for the aircraft engineers. The usage of this particular hue did not end with the surrender of Germany, as the pink trimmings remained a troop colour for the armoured troops in both Budeswehr until present and the National People's Army (armed forces of GDR) from its formation in 1956 until the unification of Germany in 1990.
And as we are speaking of pink or light purple, these colours could have been met on a battlefield far more often that one might have suspected, especially since 18th century, when distinctly coloured uniforms were commonplace. This was not always a result of choice, but rather the consequrnce of the widespread usage of plant-based dyes with mordants (fixing agents) that were not as efficient as modern ones, resulting in quick fading of colours, especially when exposed to water, what in relatively rainy, snowy and foggy Europe or North America was more or less unavoidable. But it doesn't mean that such colours were not chosen deliberately, as evidenced by e.g. cavalry units of the short-lived Duchy of Warsaw (1807-1815), where soldiers of the 1st Infantry Legion (Division) as well as those of 2nd and 8th light cavalry (Uhlan) regiment were assigned light pink (originally possibly a bit darker) distinguishing elements of the uniform (collars, sleeve cuffs, trimmings). Quick fading of the some dark red (referred to as crimson or amaranth) and blue dies was also attested in the period strongly suggesting usage of inferior plant-based dyes or dying techniques (or just attempts to save money). Pink is notably attested as a specific colour of the Royal Prussian Regiment 'Alt Kreytzen' that used distinctive pink trousers and vests (as possibly the only known military unit at the time) between early 1740s and 1788, when the reforms in the army resulted in replacement of pink elements with white ones (quite possibly as a money-saving device). In 20th century, pink was rarely used, but nevertheless it was adopted as a badge colour by several German cavalry regiments. In 1914 these were e.g. 3rd, 7th and 15th dragoon regiment, 7th Prussian mounted Jaeger regiment or Bavarian 3rd light cavalry regiment.
Thus, although the pink as a colour of the uniforms or their elements was rather unusual, it was, nevertheless, used since 18th century and the pink-like colours were not uncommonly seen as the result of fading of substandard red or violet dyes used in 18th and 19th century. Given that this colour, although uncommon, has been used continually in the German army, its presence in the Waffen-SS or Wehrmacht uniforms is nothing out of ordinary.
Mollo, J., Military fashion: A comparative history of the uniforms of the great armies from the 17th century to the First World War. Barrie & Jenkins, London 1972.
Ottmer, H-M., Stein, H-P., Symbole und Zeremoniell in deutschen Streitkräften vom 18. bis zum 20. Jahrhundert [Symbols and ceremony in German armed forces between 18th and 20th century]. Weltbild, Augsburg 1993.
