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From: dalloff@freenet.columbus.oh.us (Dave Althoff)
Newsgroups: comp.sys.apple2
Subject: Re: Hires colors
Date: 30 Oct 1995 01:34:45 -0500
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Yup.  Here's how Apple ][ hi-res colors work:

The standard hi-res screen is 192 lines of 40 bytes per line, arranged in
a very strange pattern for reasons which I will neither discuss nor
describe here, as from BASIC it is unimportant.  The oddball encoding
scheme is designed to allow for four colors plus black and white from a
one-bit color depth.  The HCOLOR= codes are as follows:

HCOLOR=0:  Black            HCOLOR=4:  Black
HCOLOR=1:  Green            HCOLOR=5:  Orange
HCOLOR=2:  Violet           HCOLOR=6:  Blue
HCOLOR=3:  White            HCOLOR=7:  White

The rules for displaying these colors are as follows:
All ODD numbered pixels on any given line must be GREEN or ORANGE.
All EVEN numbered pixels on any given line must be VIOLET or BLUE.
There is no such thing as a white point, but if any two adjacent horizontal
  pixels are illuminated, they will appear white.
The color set is determined by the high bit of each screen byte.  As a result,
  only colors from one color set my appear in any one byte.  Each byte
  represents seven adjacent screen pixels.  It IS possible to have a green dot
  next to an orange dot (with a one-pixel gap between) if the two pixels
  are not in the same byte.  If both are in the same byte, then both
  pixels will be the same color.
Note that the HCOLOR= command sets a color mask.  You can easily draw all
  six "colors" using only colors 0, 3, 4, and 7.
On a monochrome monitor, shifting the color set (i.e. changing the high
  bit) results in a half-dot shift for the byte.

I think that's about it.  For further information, if you like, I'll post
some Applesoft instructions to demonstrate how the screen works.

--Dave Althoff, Jr. 
-- 
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