help ! RFB6.0 not available in win10

hi ，

my realvnc sever&viewer software version is 7.12.1，the sound icon is gray。

my os is win10，when I use the cmd  telnet xxx:5900, then return messages RFB 005.000

but  I set the protocolveriosn is 6.0 in expert mode from sever options, 

why my win10 cmd return messages RFB 005.000？please help me ，thank you 。