fashionable pattern; trendy design
Refers to a pattern or design that is currently in fashion, often used for clothing, textiles, or accessories.
This year's fashionable pattern is floral prints.
She always wears skirts with trendy patterns.
柄 means 'pattern' or 'design' in general, without the implication of being fashionable.
Compound of 流行 (りゅうこう, 'fashion') + の (possessive particle) + 柄 (がら, 'pattern'). The exact historical derivation is straightforward; the phrase simply means 'pattern of fashion'.