A mixture of meanings, it seems. 1. denotes glans in optimum erection, prior to ejaculation, and teasing with possibility of mutual climax. 2. blue sky: her feel of contraceptive outside, when stretched under expanded glans, but definitely not yet under semen. 3. occasionally used for semen also, as, the billows blue faces (598); the fly’s blue buzz (465); the noon unwinds her blue (710); the ocean’s heart too blue (723); blue sea noon wilt welcome me? (162); the breadths of blue (128); the heaven below obscured with ruddier blue (756)