It’s possible indeed. First of all the client you saw probably was a Channel commander. The speaking colour is yellow thought, the non-speaking colour would be orange.
The second solution would be using either a custom icon pack. That requires a bit of work, but still should be doable.
Simply
head to the installation folder of \TeamSpeak 3 Client\gfx,
copy the icon pack you use (most likely either default_colored_2014.zip or default_mono_2014.zip),
paste it into %AppData%\TS3Client\gfx,
unpack the zip file into the folder,
rename the folder into something easily rememberable,
open the unzipped folder, and either
rename player_commander_off.svg into player_off.svg and player_commander_on.svg into player_on.svg / do the same vice versa (requires a bit of shuffling work), or
recolour player_off.svg and player_on.svg to your liking (requires editing software that supports svg files)
Start TeamSpeak, open Options, head to Design, and choose the newly created Icon Pack under Icon Pack.