HTML fields will only show up for you if you have a 64 bit OS and are using a 64 bit Service Desk Console. Same goes for 32 bit OS using a 32 bit Service Desk Console.
Develop your one touch console on a 64 bit OS.
I was experiencing the same. I could not see some description fields in the Process Designer. I discovered that I was running the 32bit client on my 64bit computer and OS (the shortcut that had been created on my desktop was pointing to the wrong console.exe, should have been consolex64.exe). As soon as I started running the 64bit client this was no longer a problem.