I think there was some sort of color support prior to System 7.
kagis
https://en.wikipedia.org/wiki/Macintosh_II
System 6 includes QuickerGraf (originally QuickerDraw), system software used to accelerate the drawing of color images on the Macintosh II.
Hmm. Apparently System 4 had color support, which is earlier than I expected.
...it wasn't until two years later in 1987 that Apple introduced color with the release of the System 4 & the Macintosh II.
Here's a photo of a IIcx with a color display:
