watchman goby pairing. need helppp!!!

[romsoccer12]

right now i have a yellow watchman goby in my tank, all yellow.
the LFS jsut got a yellow watchman goby that was grey. my LFS said the greys are the males and yellows the female so i can pair them.

is this correct? i have a grey in QT ready to be introduced to DT with the yellow, should i worry?

 

[romsoccer12]

well i added the grey one. he was awesome adjusting to the tank. already ate some sand, ate a little food too.
after a couple hours they saw each other and had this huge display of who could open there mouths more and than the grey one swam in the yellow ones burrow and now i cant see them anymore
plz i need some advice