A myriad of theories to account for color phenomena were in circulation in the early seventeenth century. The status, goal, and content of these ideas differed as did the range of phenomena they addressed. Starting with the journal of Isaac Beeckman (1588–1637), this project enquired into the features and functions of conceptual reflections upon color experiences. Beeckman’s pioneering thinking played a crucial role in the intellectual development of René Descartes (1596-1650), while at the same time differed from Descartes' ideas in a fundamental way. These differences illustrate the wide variety of early corpuscular conceptions of color that cannot be reduced to the mechanistic variety envisioned by Descartes. Broadening the view to include yet further instances of corpuscular thinking, a stratification of conceptualizations was proposed that is grounded in various problem contexts rather than philosophical doctrines. In this way this chapter proposed a way to find a place for "theory" in the new historiography of optics, positioning it in relation to material, manipulative, and artistic color practices.