There was a time when pink was considered a lighter shade of the masculine red and thus appropriate for boys before they became men, and blue was associated with young girls.  Times have changed and it has to do with creative marketing, as related by Terry O.

Fingering weight

206m/225yd skeins

65g/2.3oz

3-3.5mm/2.5-4US

26-30 sts/10mm/4"