In the test mode you are actually turning on every 3rd channel, ie. 1,4,7,10 etc for red and 2,5,6,11, etc for green, etc and then all channels for white. That is just the way that the test mode was written years ago. So if you add 2 to the first channel of a string and divide by 3 see if it comes up as an even number. If not then the only way you solve this is to adjust your starting channel number. But all your strings and controllers also have to be set for RGB so there may be multiple hurdles to getting what you want / think you should get.