Answer could be many things but I dont think it is the software, Questions back, Are they the same brand of floods? power supplies?
First I would look at power and type of LED Floods they are. But then again you could just have too many floods out now, meaning now that you have so many floods that the colors blah together.
This brings us to the term that sometimes LESS IS MORE. Not knowing the size of your yard/stage I would look at the over abundance of lights. When just having 12 floods, colors were popping, bright and vibrant but then add another 16 to that mix and the colors seem blah, dimm and just simply plain. Give you an example, Take a blue crayon and just put 1 line down, nice blue color huh? now on that same line mark it 4 more times, a little darker but still a nice color of blue. now do it 7 more times on the same line, darker yet but you still see the blue. now do it 16 more times and see what you get, kinda blah and almost to dark to see the blue. Im sure you see where im going with this. So again not knowing how large your canvas is I would first look at power consumption then I would look at how much is too much. 12 looked bright and popping so try adding just 4 more and see what you get, then 4 more and so on until you get the balance your looking for. Again not knowing the size but just by what you say I cant see you adding more then 10 more and even just 8 out of the 16 should do ya, Also remember Location, location, location. Mix em up, some on the roof , some on the ground OH wait , Heres a prop for ya, leave the 12 where they were and the new 16 floods have 2 8 flood RGB fire sticks. Just a thought.
I know this was a long reply but I hope it helps.