Heavily used in classical poetry —
满园春色 ('garden full of spring colors') and
春色满园关不住 (Ye Shaoweng's famous Song-dynasty line, 'spring scenery fills the garden, the wall can't hold it in') are stock allusions. The figurative sense ('blush, flush') often hints at romantic feeling, so
一脸春色 can mean 'glowing with springtime — and maybe a little something else'.
