rednessOf+little+leaves+opening+stickily.

When the leaves of spring are mentioned, one could think about fresh green sprouting up from the ground and becoming ready to absorb sunlight. That is not however the imagery that Millay has put into this line because the leaves are red; more often associated with fall. The leaves she is talking about might not necessarily be the conventional idea of green leaves, but instead petals or flowers opening and blooming.