Displaying all 11 of the CoCo’s 8 colors…

I was today years old when I learned that the colors of the CoCo’s high resolution graphics screens are the same as the colors of the text mode semigraphics.

I knew that the CoCo’s MC6847 video chip could produce eight colors on the text screen. The manual describes them as green, yellow, blue, red, buff, cyan, magenta and orange. (Okay fine. It is really nine since you have black as well.)

These eight colors are shown in an example program in the Radio Shack quick reference guide. You will notice this does not draw a black strip for the 9th color – I guess theblack border is enough of a color test for black.

Color Adjustment Test Display, Radio Shack TRS-80 Color Computer Quick Reference Guide, page 55.

On the text screen, these colors are part of the character set. Each character block can have colors set in a 2X2 grid, with one color plus black per character location.

I also knew that when you went in to one of the 4-color high resolution graphics modes, PMODE 1 or PMODE 3, you had two sets of colors available.

In SCREEN 1,0, you get a green border, and four colors – green, yellow, blue and red.

In SCREEN 1,1, you get a white border and four colors – white, green, purple and orange.

I wondered if it might be possible to write some code to switch graphics modes and get all of these colors on screen at the same time. I created a sample of what it might look like … and then I realized these colors are all the same!

For SCREEN 1,0 you are getting the same green, yellow, blue and red that the text screen has.

For SCREEN 1,1 you are getting the same buff, cyan, magenta and orange that the text screen has.

“I feel dumb I never realized they were the same colors!”

– Allen

Here is the program I used to switch between them to get my screen shots…


10 CLS0:PRINT@4*32,;
20 FOR R=0 TO 3
30 FOR C=0 TO 3
40 PRINT STRING$(8,143+C*16);
60 FOR R=0 TO 3
70 FOR C=4 TO 7
80 PRINT STRING$(8,143+C*16);
95 GOSUB 1000

100 ' COLOR SET 0
120 FOR C=1 TO 3
130 COLOR C:LINE((C-1)*64,0)-((C-1)*64+63,0+47),PSET,BF
140 NEXT
145 COLOR 0:LINE(3*64,0)-(3*64+63,0+47),PSET,BF
150 GOSUB 1000

200 ' COLOR SET 1
220 FOR C=1 TO 3
230 COLOR C:LINE((C-1)*64,144)-((C-1)*64+63,144+47),PSET,BF
240 NEXT
245 COLOR 0:LINE(3*64,144)-(3*64+63,144+47),PSET,BF
250 GOSUB 1000

999 END

1000 IF INKEY$="" THEN 1000

This means, even with the two different graphics mode color sets, you still only get those eight (or nine, including black) colors to play with.

BUT… technically there are more color than that. The color of the text characters is not black — but some kind of dark green (see the square I drew to the left of the text, below):

And, there is an alternate color set for the text screen that has a different color for the text, and a different color for the background.

Or does it?

Admittedly, the usefulness of the text colors is limited since you cannot do anything with those colors except put text characters on the screen with them… (More on this in a moment…)

Having the alternate background does seem useful. Or is it?

I was today years old when I learned that the alternate background text color (SCREEN 0,1) is the same as one the orange primary color (CHR$ 255), just as the normal background text color (SCREEN 0,0) is the same as the green primary color (CHR$ 143)!

Sample code:

10 CLS
20 PRINT "----SPACES-----";CHR$(128);CHR$(128)"---CHR$(143)---";
30 FOR R=1 TO 14
40 PRINT STRING$(15," ");STRING$(2,128);STRING$(15,143);
60 PRINT "----SPACES-----";CHR$(128);CHR$(128)"---CHR$(143)--";
70 IF INKEY$="" THEN 70

80 CLS
90 PRINT "----SPACES-----";CHR$(128);CHR$(128)"---CHR$(255)---";
100 FOR R=1 TO 14
110 PRINT STRING$(15," ");STRING$(2,128);STRING$(15,255);
120 NEXT
130 PRINT "----SPACES-----";CHR$(128);CHR$(128)"---CHR$(255)--";
140 SCREEN 0,1

150 GOTO 70

So I guess that, even with the alternate color set, you still only have the same eight colors plus black – plus whatever color the text is, which you cannot use.

Or can you?

Lowercase is represented by inverted video, and although you cannot PRINT a lowercase space, you can POKE it to the screen.

POKE 1024,32

That will poke the inverted space to the top left of the 32 column screen.

And that is another color!

Let’s update the color bar…

10 CLS
20 FOR R=0 TO 15
30 PRINT @R*32,"X";
40 FOR C=0 TO 7
50 PRINT STRING$(3,143+C*16);
70 PRINT STRING$(3,128);
80 POKE 1024+32*R+28,32:POKE 1024+32*R+29,32:POKE 1024+32*R+30,32
90 POKE 1024+32*R+31,ASC("X")
100 NEXT
110 IF INKEY$="" THEN 110
120 SCREEN 0,1
130 IF INKEY$="" THEN 130
140 SCREEN 0,0
150 GOTO 110

This program will print vertical bars of the 9 semigraphics block colors – black, green, yellow, blue, red, buff, cyan, magenta and orange.

It then uses POKE to set three blocks on each line to an inverted space (“lowercase space”) to show that color. The end result is ten colors on the screen:

Look closely on the right — there is black bar, then a bar using the text color (inverted space), then the bar of Xs.

Pressing a key flips to the alternate color mode and that helps make that last column easier to see:

This means if you wanted to do glorious 32×16 color graphics, you actually have 11 colors you can choose from, though that would be the ten at a time (nine base colors plus the text color of the mode).

But I expect many of you already knew this.

4 thoughts on “Displaying all 11 of the CoCo’s 8 colors…

    1. Allen

      I do not see the 8 semigraphics colors changing, at least in XRoar. What do you see? It has been too long since I saw a “real” TV set hooked to a CoCo. My final years with my CoCo 3 were using an FPGA-VGA interface and it was creating colors based on the RGB signal. But, as I’ll try to write about soon, the CoCo 3’s choice of pallet colors for these graphics seems to be … wrong. Maybe as close as it could get, but certainly different than what the CoCo 1/2 had. We just were beyond using those modes by the time we got to a CoCo 3, I guess?

  1. Sean Patrick Conner

    The first two lines look like orange on burgundy, and the cyan blocks look more pale green to me. Also, the orange of the background is lighter than the orange blocks. But I’m using an older version of XRoar so it might just be me.

    1. Allen Huffman Post author

      The colors change based on selecting S-Video output (simulating that kind of add on), or red/blue versus blue/red artifact mode. I suppose we’d need to see a CoCo with a composite video mod on a good calibrated composite monitor to use as reference.


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