Last days there was a server restart. This resulted in the number "active players" (listed in ladder) to go from 3k to 1.5k. This results in an immediate decrease of ranking (for example for me, the next game I would loose I would become silver). I personally think this yo-yo with the rank color based on server restart to be kind of annoying considering the rank system should have "inertia".
Of course that does not mean that there is no smurf wave, but the re-coloring can contribute to the noise and chaos. I think the best is to check their actual WHR value, not the color. I have seen yellow or silver with a WHR of 2200 or 2300 in a game some weeks ago, so the system might work as expected.