[AlexW]

""... note the confines of the colours, that is of the red MabF, of the orange acdb, of the yellow cefd, of the green eghf, of the blue gijh, of the indico iklj, and of the violet kGAl."

dr_lew. your way over my simple head, but if it validates what I was taught, it is fine for me :)

[dr_lew]

The letters refer to a simple diagram:

Each set of four letters designates a rectangle according to the geometric notation that was second nature to Newton and his contemporaries. Of course, his diagram is not in color!