i have the Browns ones from the mobs but nether are poping up. I've made 10 soul sand and no mushrooms. I even waited a few minutes between each soul sand and nothing. I used to average 2-3 between each. Don't know what you guys average is.
So, did a short experiment for you. And it works. Used just four bottles of water. Out of the 4 times I put the water in and it turned , first time - one red, second time, one of each, third time - neither, fourth time - brown. Random but it does pop up.
Also works if you plant a shroom on the mycellium and water it - it'll spread.