DVM:

$C058 - Disable 80 column input
$C059 - Enable 80 column input
$C05A - Enable red
$C05B - Disable red
$C05C - Disable green
$C05D - Enable green
$C05E - Disable blue
$C05F - Enable blue

Yes the enable/disable of red is the reverse of green & blue. 

DVM II:

$C080 + slot * 16: 
  0: Enable red
  1: Disable red
  2: Enable green
  3: Disable green
  4: Enable blue
  5: Disable blue
  6: Use upper video port
  7: Use lower video port
  8: Partial mono
  A: Mono hi-res
  D: Intensity