RGB LEDs can produce any color inside their spectrum, the same as your
computer monitor. It is basically limited by how pure the red, green,
blue are, and the maximum intensity of each.

I'm thinking "all possible colors" means any color. Thing is, you can
do several things:

-No PWM, plain Red,Green,Blue only, cycling all three.
-No PWM, combinations: Red,Green,Blue,Cyan(Blue+Green)'light
blue',Magenta(Blue+Red)'purple',Yellow(Red+Green). Plus white and/or
black if you like. Total 8 colors. This is just 2^3.
-PWM, middle intensities (half red, etc). Many more colors (3^3=27).
-PWM, more intensities. You can do 4 intensities each
(0%,33%,66%,100%) which gives you 4^3=64 colors.

etc all going up to what would be hicolor in PC-speak (32768 colors,
which is 5bits red, 5bit blue, 5bits red (32 colors each, 32768 colors
total)
Or truecolor, millions of colors (8bits each, 256 possible intensities
each, total of 16777216 colors).

The program for N-colors PWM (N colors for each channel, not total)
for RGB would be something like

each timer tick/overflow/interrupt/whatever
    increment PWMCnt
    if PWMCnt>=(Ncolors-1)
        PWMCnt=0
        Rvalue2=Rvalue
        Gvalue2=Gvalue
        Bvalue2=Bvalue
    endif

    if Rvalue2>PWNCnt
        Rpin=1
    else
        Rpin=0
    endif

    if Gvalue2>PWNCnt
        Gpin=1
    else
        Gpin=0
    endif

    if Bvalue2>PWNCnt
        Bpin=1
    else
        Bpin=0
    endif

return

And then, in the main loop, run something that changes Bvalue, Rvalue,
etc. Note that I cache the value to prevent changes during a PWM cycle.

Try with several values for the timing. For example, for a 256 values
per channel PWM, try something like each 1ms and go lower until the
flickering disappears. Usually 64 values per channel will suffice, and
will flicker much less and won't need the loop run so often.

To cycle through all colors (hues, no black or white in this example,
no brightness or saturation, just hues) you can run something in the
main loop that does, for example:

(start with red=100%,blue=0%,green=0%)
repeat forever:
    (total color is now red)
    ramp green from 0% to 100%
    (total color is now yellow)
    ramp red from 100% to 0%
    (total color is now green)
    ramp blue from 0% to 100%
    (total color is now cyan)
    ramp green from 100% to 0%
    (total color is now blue)
    ramp red from 0% to 100%
    (total color is now magenta)
    ramp blue from 100% to 0%
    (total color is red again)
end repeat

note that after a ramp the color remains at the end value, i.e. "ramp
red from 100% to 0%" does NOT mean touch the blue or green channels,
just leave them as they were after the last ramp. If you want to avoid
timers, and you do not intend to do anything else other than cycle the
LED, you can do something like the following, in which case you can
also remove the caching of the values in the PWM subroutine:

subroutine ramp(*channel,from,to):
    *channel=from
    repeat until *channel>=to:
        increment *channel
        repeat N times: (N depends on the speed on the effect, how
much each separate color stays before changing into the next tick, in
units of PWM cycles)
            call PWM subroutine
            delay (this is the PWM delay)
        end repeat
    end repeat
end subroutine

main program:
repeat forever:
    ramp(&Gvalue,0,max_color)
    ramp(&Rvalue,max_color,0)
    ramp(&Bvalue,0,max_color)
    ramp(&Gvalue,max_color,0)
    ramp(&Rvalue,0,max_color)
    ramp(&Bvalue,max_color,0)
end repeat

(where max_color equals Ncolors-1)

Note that I use */& the C way, since passing the value to the
subroutine won't do any good, you want to be able to CHANGE the value.
Or make 3 ramp subroutines, one for each color, or pass a value 0 for
red, 1 for green, 2 for blue, or whatever.

Of course the purity of the colors will be affected by the different
intensities. I recommend hooking up the outputs from the PIC to some
transistors and adding a pot to the base to be able to adjust
individual brightness.

HTH,

-- 
Hector Martin (hector@marcansoft.com)
Public Key: http://www.marcansoft.com/hector.asc

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