In color theory, a purple is defined as any non-spectral color between violet and red (excluding violet and red themselves). The spectral colors violet and indigo are not purples according to color theory, but they are purples according to common English usage since they are between red and blue.
Apex Learning was started in 1997 by Microsoft co-founder Paul Allen on the idea that online courses and test prep, which were already succeeding in higher education, could be applied to K-12.
In 2015, Khan Academy and the College Board (the company that designs and administers the SAT, PSAT, and AP tests) teamed up to provide free SAT study tools, which is what this guide will be focusing on. (Since the College Board doesn't administer the ACT, Khan Academy does not offer materials directly geared towards ACT prep.)