1550s, "figure of speech" (a sense now obsolete), from Medieval Latin schema "a shape, a figure, a form, appearance; figure of speech; posture in dancing," from Greek skhēma (genitive skhematos) "figure, appearance, the nature of a thing," which is related to skhein "to get," and ekhein "to have, hold; be in a given state or condition" (from PIE root *segh- "to hold").
By 1610s as "linear representation showing relative positions pf the parts or elements of a system" (especially in astrology). The sense "program of action" is by 1640s, also "outline, draft of a book, etc."
The meaning "plan of action devised to attain some end" is by 1718, and unfavorable overtones (selfishness, deviousness) began to creep in to the word after that time. Meaning "complex unity of coordinated component elements, a connected and orderly arrangement" is from 1736. In prosody by 1838. Color scheme is by 1890 (in Milton Bradley Co.'s "Color in the School-Room"); earlier scheme of colour (by 1877).