function to control an rgb led

Sure - if you're doing that, it sounds like you don't need the colors array at all.

• set colFrom to [0,0,0] - to start the sequence from black
  
• set colFade to 0 (to reset the fade to start from the beginning)
  
• set colTo to [a,b,c]
  

• Then, in the if (colFade>=1) if statement, replace what's there with:

  colFade = 0; // restart fade again
  colFrom = colTo; // fade from what we faded *to* last time
  colTo = [....]; // your random values
  

You could also look at using this function: http://www.espruino.com/Reference#l_E_HSBtoRGB

Probably what you want is a random hue, but keeping the same brightness and saturation, and that function will help you. You will however need to extract the RGB values from the 24 bit number, which is a bit cryptic:

var c = E.HSBtoRGB(Math.random(),1,1);
colTo = [ (c&0xFF)/256, ((c>>8)&0xFF)/256, ((c>>16)&0xFF)/256 ];